Did you upgrade an existing installation?
Most do this - but the switch from Plasma 5 to Plasma 6 may have left some incompatible configurations.
You appear to have booted xorg - please try with Wayland.
If you have not already done so, the first thing is switch the DP port perhaps the event required to trigger the system to find the display.
It is not possible to provide a one-stop answer - you will have to go over some troubleshooting steps. Please see NVIDIA/Troubleshooting - ArchWiki for more info as this is likely to apply for Manjaro as well.