When I start Ultimate Doom, all I can see is the title card, but no menu. I can hear the demo playing, and when I press the arrow keys I can hear the menu sounds. If I press enter a few times I can hear a game starting and if I press ctrl I can hear the gun shooting, but I'm still just seeing only the title card image.

Ok, I think I solved it.

In the game folder, I found the dosbox_doom.conf file. I opened it in notepad, and I changed the line:

output=surface

to:

output=opengl

and it seems to work fine now.