Dosbox-x - how to get fullscreen?

General system Newbie
1

Can’t take a screenshot, but I get a fullscreen black window with a large postage stamp window. Relevant config line changed:

fullscreen        = true
fulldouble        = false
fullresolution    = 1920x1080
windowresolution  = desktop
windowposition    = -
2

2 f’in hours. Changed to opengl, works:

output            = opengl