I have an optimus laptop (AMD/NVIDIA) and use an external monitor. The external monitor is detected and works, but Gnome 42 Display Settings only allow to Join or Mirror the monitors, but not use Single monitor. On top of that, the settings do not persist through reboots.
I want to use only the external monitor, when it is connected, and would like the system to remember my choice/settings.
On a related note, how can I enable fractional scaling?
I believe the difference must be the use of Optimus switch.
I would try without it.
A related factor is that the external output is connected to nvidia dgpu.
Also some firmware/BIOS apply some automation on the Hybrid setup. Then, using an additional software automation may conflict and produce strange/uncontrolled results.