Hallo,
I try to make a custom display work (7" 1200x1920, yes this way, not 1920x1200). So far i managed to get it working with imported overlay from raspian (vc4-fkms-v3d) and manual hdmi-timing in config.txt . This way i get a full filled display but cant rotate it 90° as needed, because this display is in portrait mode (1200x1920).
If i disable overlay and use cvt settings instead in config.txt (hdmi_cvt= 1200 1920 60 5 0 0 0) i can use the display_hdmi_rotate command to rotate the output as wanted, but now framebuffer is set to 1280x1200.
So the overlay causes right resolution but no rotation, hdmi_cvt causes rotation but wrong resolution.
Is there any other way? e.g. ∕opt/victronenergy/gui/start-gui.sh