Ok, it’s this:
/lib/udev/rules.d/80-pm-nvidia.rules:ACTION=="add", SUBSYSTEM=="pci", ATTR{vendor}=="0x10de", ATTR{class}=="0x030000", ATTR{remove}="1"
it’s removing the nvidia gpu from the bus. The rest of the file are rules to prepare for render offload.
This looks like something changed in Ubuntu’s prime-select/nvidia-prime again, don’t really know what’s the point of doing this… Please post the output of
sudo prime-select query