I’m having this really hairy confusing issue. I have a lenovo P73 laptop that comes with hybrid graphics (it can also be configured in the bios to be discrete only). In hybrid mode, the laptop screen is connected to a Mux that in hybrid mode takes the input from the intel igpu. All other outputs are always driven by the nvidia card (TU104GLM - Quadro RTX 4000 Mobile). Connecting a HDMI screen works perfectly (either in reverse prime mode - with the reported laggyness on the Nvidia connected screens, or when using the nvidia driver as primary and ofloading to the iGPU for the laptop display).
I do however also have a usb-C to vga displayport alternate mode dongle. If I plug in this dongle after boot it will be recognized (the plugging in detected and the software (KDE kscreen) will do it’s autoconfig magic. However, if the dongle is plugged in at boot, the screen will not be detected except after unplugging/plugging in the screen.
Additional information is that I have blacklisted the kernel typec modules (typec, typec_ucsi ucsi_acpi and ucsi_ccg). If those are loaded (or loaded into the kernel) the plugging in is unreliable (it will sometimes detect, sometimes not). Attached are the result of alling bug-report once working nvidia-bug-report.working.log.gz (2.9 MB) the kernel configuration config.gz (36.2 KB), dmesg: dmesg.gz (34.3 KB).