Hi,
I have the same issue on a laptop Lenovo Legion 5 (cpu Ryzen and Nvidia card).
On the live iso no problem when a second screen was connected with HDMI.
I installed also the Nvidia driver with DoFlicky, so for my card "nvidia-common 560.35.03".
I found a solution to install CUDA and DaVinci Resolve, but for the screen I have no idea for this issue.
Here some screenshots (fastfetch nvidia-smi nvtop ...etc)
Any idea ?