JoeViking245

Didn't watch the video to see what all it covered.  But this article from the LaunchBox Strategy Guide may help also.  (It covers emulators and their portability, required dependencies and maybe some other goodies.)
Moving Your LaunchBox Instance to a New PC - LaunchBox

Not really sure what to make of that, but I'll go with 'if you went to YouTube and played a video, you'd hear its audio.'  
I asked about the MAME version because know there were some audio issues with release 0.278.
The only reason MAME would stop having audio output is if a setting was changed (in MAME) or your speaker volume is turned down or muted, or your speakers were turned off. Since you indicated your sound is working fine with everything else, I'm inclined to say it's a setting in MAME itself.

The only thing I can help with is sharing my process.
My test:
Installed a fresh copy of LaunchBox 13.22 Closed the initial Add Games popup I don't think Download Bezels options popup via this wizard (could be wrong) Though they can always be added later via Download - Metadata and Media Tools - Manage - Emulators - Add RetroArch - Download OK - Close  
Tools - Import - ROM Files - Single Platform selected my Atari 2600 folder, followed default prompts Checked Download Bezels (selected default Theme Bezels) finished the process to import Selected Adventures of Tron and clicked Play.

The only thing in RetroArch I did go in and manually change was Settings - Input - and set Confirm Quit to Off.  Otherwise, nothing in RA was changed/setup/modified/etc.
The bezels are found in \LaunchBox\Emulators\RetroArch\overlays\GameBezels\Atari2600\[.png and .cfg files]

Select a game, then press Ctrl+A (to select all games in that platform).  Then Tools < Download < Update Metadata and Media for Selected Games...
Sticking with MAME (Arcade), I suggest selecting Advertisement Flyer - Front in leu of Box-Front as arcade cabinets weren't shipped in 'boxes'.  Crates, yeah.  
Videos and Manuals only come from EmuMovies.  The LaunchBox Database doesn't have those.  When you purchase you LB license, I believe they also provide a discount code for an EmuMovies subscription (which is required for downloading from within LB).
 
Again, sticking with MAME, yes.  It's easiest to manage if your emulator(s) are installed in /LaunchBox/Emulators/.  Then it's just a matter of moving the /LaunchBox/ folder.
Some emulators, by default are not portable. They'll store some of their data in your C:\Users\JoeViking\AppData\emu_name\ folder. (there, or in \Documents\, or somewhere else).  But most can be made "portable" so their data is stored within the emulators folder.  Varies by emulator.
 
Regarding bezels for other consoles that should have them, that will be console specific.  (aka need more info)  But that's all outside of my wheelhouse.  So the "more info" would be for someone else. 😁

They were both found here.  Make sure your Platform is set to Windows.  May also try to force update your local database.
Tools < Download < Force Update Games Database Metadata...
 


 
 

Edit your PacMan game. Under Emulation, check the box Use Custom Command-line Parameters. in the space below it, add -plugin pactrainer.
This will actually send the command mame -plugin pactrainer pacman. But should work just the same. 
If you use the LaunchBox Pause Menu for Arcade, shame on you.  But if that's your thing, you'll need to add -keyboardprovider dinput -plugin pactrainer for it to work.

Give this a read. Hopefully something in there will resolve the issue.
Plugin Access Denied Error - LaunchBox

The default location change in version 13.21 with the advent of Media Packs.  You can find more information about them here:
LaunchBox Media Pack Feature – Version 13.21 - LaunchBox

(I'm guessing you're meaning /LaunchBox/Emulators/RetroArch/)  No. It's not. 
If for some reason it truly is missing on yours, then I'm surprised RA even opens. As in it's probably a corrupt install.  If that's the case, have LaunchBox reinstall it for you in Tools - Manage Emulators. 
Otherwise, right-click a game using RA and follow the red boxes...

Update your local database
Tools < Download < Force Update Games Database Metadata...

Anything's possible.
To test, you could try removing the contents of your emulators \UserData\ folder.  Then copy the contents of your \AppData\Roaming\BigPEmu\ folder into it.  Then use the %romfile% -localdata parameter(s).
If that works, you can remove the /AppData/Roaming/BigPEmu/ folder.

Clear Logo folder location changed as of version 13.21.  Can read more about it here:
LaunchBox Media Pack Feature – Version 13.21 - LaunchBox

If you had LaunchBox install MAME for you, there should be some scripts in the Reset, Save and Load sections.
 
...and if those scripts had been in there, you could look at the one for Save, where it takes a modifier key and another keypress to activate.  Modify that script to suit your needs and you'd get
Send {Alt down} Sleep 50 Send {r down} Sleep 50 Send {r up} Sleep 50 Send {Alt up} The key here (no pun intended) is setting a Key Delay which is needed for some emulators.  Essentially, you're causing a more pronounced key press(es).
I haven't tested this in Supermodel because like any Arcade game, I don't save.  We call it "old school".   But I suspect it will work.  

For games that don't use a [traditional] emulator such as Steam, you can override the startup time on a per game basis or Bulk Edit the games and set them all at once.
To bulk edit them, select all your Steam games (e.g. in the Windows platform, click one then press Ctrl+A) then press Ctrl+E to start the Bulk Edit Wizard. 
For the Field select Startup Screen - Enabled and check the box.  When prompted for more changes, select Yes, I would like to make more changes.  For the Field, select Startup Screen - Load Delay. Then adjust the value accordingly.

When you select multiple game then go to Tools < Download < Update Metadata and Media for Selected Games..., you want to leave checked Search for game information in the local metadata database (recommended).
On the next screen (and 2 if you have an EmuMovies account) select the image you want to download.  
Then select Yes, but do not replace any existing fields or media (recommended). And Finish.
 
This will only update the games you selected.

It's because you have emulation enabled.  So it's trying to pass the script to RSPC3.   Go to the Emulation section for the game and uncheck Use Emulator.

The Default Theme has "built-in" fallback images that it looks for.
Steam Screenshot Epic Games Screenshot GOG Screenshot Amazon Screenshot Origin Screenshot Backgrounds Screenshot - Gameplay You can change (add or remove or re-prioritize) the Background Image Priorities under Tool - Options. (This is where you might add Arcade-Marquees).
 
It's hard coded into the theme.  But has an easy work-around.
Make a copy of the \LaunchBox\LBThemes\Default\ folder In your "copied" folder, open the file \Views\GameDetailsView.xaml with any text editor Look for <!-- TOP BORDER OVERLAY --> Delete it and the next line Save and close Open LaunchBox Set the Theme to-use to the "copied" folder Theme Name (which may be "Default - Copy") Instead of editing that file, you might be able just delete the image file \LaunchBox\LBThemes\Default - Copy\Images\Overlay.png. 
I don't know if simply deleting image file will throw an error or not. But editing the xaml will for sure work.
Regardless, you will need to make a copy of the Themes folder in order to make any changes or file deletions. 

Do you have the corresponding .chd file for the game?  Is the folder holding the CHD file in the same location as the ROM?
/Games/Arcade/sf2049.zip
/Games/Arcade/sf2049/sf2049.chd

It can be.  But mostly (aside from programming knowledge) time.
You can always Request A Feature (above under Help & Support).  Be specific.
See here and remember to upvote it as deemed necessary.
Feedback - LaunchBox

The error message seems to be missing some data. aka can't see the whole message to be able to best decipher the actual cause.  For future, you can copy and paste the whole text that's in the message.
Lately, that type of error message depicts that's there's an issue with a 3rd party plugin. You can try removing them from the Plugins folder. (the 3rd party plugins, that is. Not LaunchBox's plugins)
Or, to change the Theme, you can edit /Data/BigBoxSettings.xml.  Look for <Theme> and change the value to Default.  e.g.  <Theme>Default</Theme>

Assuming with your premium license you've updated to at least v13.21, you can read about the new locations here:
LaunchBox Media Pack Feature – Version 13.21 - LaunchBox

System Menu < Options < General < Skip Game Details Screen
But this way you'll never see the Game Details screen unless you change it back.
Instead, you could also map a button or key to "Play" the selected game (skipping the Game Details).
System Menu < Options < Controller Mappings < Play

According to some recent posts on LaunchBox Discord and a 2 year old post on LaunchBox reddit, you need to add the games to 3dSen itself, 1st. 
It then saves game info into a rom.json file.  Located somewhere in [%appdata%\..\LocalLow\Geod Studio\3dSen]
After the games have been added, open the json file with any text editor.  An example node looks like:
"id": "64", "romPath": "C:\Nintendo NES (3dSen) Games\\Mega Man 3 (USA).nes", "title": "Mega Man 3", "lastTime": 1692883659 Look for the game and get the id number.  Edit that game [that you've already imported into LaunchBox] and in the Emulation section, it should already be set to use your 3dSen emulator [that you've already installed into LaunchBox].  Check the box for Use Custom Command-line and in the box below it, put in -id=64  where "64" the id number you found.  Save. Close. Play
Yes. You'll have to do it individually, for each game.
 
For me, this is all hearsay.  But @ci2own says it works.   

Without overthinking it...
$Esc:: { WinClose, ahk_exe {{{StartupEXE}}} Sleep, 5000 WinClose, ahk_exe {{{StartupEXE}}} }  

You're not blind.  Or... we both are.  
Depending on what you wired the Mute/Unmute button to and what mode it's in, you might be able to create an AutoHotkey script that you have run when you start LaunchBox and/or Big Box. For this (possible) option to work, you need to know what your button is mapped to.
Example: Your encoder in keyboard mode and you have the button mapped to "M" (again, just an example).  The script would look like
m::Send {Volume_Mute}  
 
To use the built Pause Screen, set the pause button.  Note: LB and BB require separate mappings.
LaunchBox:   
Keyboard Mode:  Tools < Options < Gameplay < Game Pause XInput Mode:   Tools < Options < GameControllers < Mappings - Show Pause Screen Big Box:   
Keyboard Mode:   System Menu < Options < Keyboard Mappings - Show Pause Screen XInput Mode:   System Menu < Options < Controller Mappings < Show Pause Screen  
Once that's all dialed in, take a look around at all the other cool things you can do from within the Options Menu(s).