I just got the app and faced the same issue, so I tried launching it with Xwayland, and that works! It will break HiDPI since Xwayland doesn't support it yet (blurry appearance), but at least it launches and saves you from having to sign into the X11 session.
I notice that in Player.log, the application cannot even start logging anything, it outputs one line, and that states my screen resolution is 0x0@0hz. Now I'm no expert, but I think my resolution affords me a bit more screen real estate than that.
Anyways:
To launch Asset Forge with Xwayland, you need to set the following environment variable: SDL_VIDEODRIVER=x11
Example in a terminal, from the Asset Forge folder: SDL_VIDEODRIVER=x11 ./Asset\ Forge.x86_64
By the way, thanks Kenney, this app is super awesome!!