Can't change screen resolution Ubuntu 22.04

after working for a long time with reduced resolution on my QHD laptop, the screen suddenly remained black after logging in and the mouse cursor was missing.
To boot in native resolution, I deleted the monitors.xml.
The problem ist fixed, but returning to fullhd makes the cursor disappear and the screen goes black.
Can someone help ?

What sort of graphics are you using? nvidia?

Nvidia GTX 3600 ist installed,
but normally Radeon RX Vega 8 is working