Hello there! I found the solution.
I had the same problem as everyone else.
1st - Make your profile public
2nd - Get your Steam Web API Key
3rd - When importing, make sure you are reading correctly because the 1st thing LaunchBox asks is for your Steam URL Profile, that means:
3.1 - You need to go to your profile
3.2 - Click on edit profile in the right upper corner
3.3 - Find the custom URL inside your profile configuration and paste it in the program.
OBS: You can't put your custom name and " / " at the end of it, only your custom URL
3.4 Put your Steam Web API Key.
The rest is self-explanatory, select the media you want to download and have fun