[Fusion fullscreen]

There's an easy fix for this

Retro808 is correct but a little confusing here's the easier process

Select Kega as your emulator

Got to the "Tools" menu in Launchbox

Select "Manage Emulators"

Edit Kega

Got to the "Associated Platforms" tab

And here you'll see your fullscreen problem clearly

Just delete the -fullscreen parameter for each console and Kega will not go fullscreen

I'm not a big fan of Retroarch in Launchbox; and this worked well for me

 

[Kega Fusion Windowed]

There's an easy fix for this

Select Kega as your emulator

Got to the "Tools" menu in Launchbox

Select "Manage Emulators"

Edit Kega

Got to the "Associated Platforms" tab

And here you'll see your fullscreen problem clearly

Just delete the -fullscreen parameter for each console and Kega will not go fullscreen

I'm not a big fan of Retroarch in Launchbox; and this worked well for me