I acquired a nice 23" cinema display with ADC connector for my G4 Powermac. According to this site everymac it supports 800 by 500, 1024 by 640, 1280 by 800, and 1920 by 1200

Currently I have it Ambient on the 1900 by 1200 screenmode but if I want to run Quake I seem not to be able to choose 1900*1200 ingame or other relevant screenmodes so it never fits the display or worse. How do I solve this. 1900*1200 seems to be the only screenmode I have in monitorprefs.

What Quake I port are you using? GLQuake by Kiero allows you to adjust the resolution to your needs, and MorphOS Screens preferences have nothing to do with that.

Those monitors lack the capability to scale signals just like the buildin displays found in laptops.

Under OSX scaling is done in the GFX-card, something MorphOS doesn't offer in this setup.

I did a typo. I have quake 2 and 3 installed and wolfenstein. All three have problems.

So the cinema display is useless or ?