I am on nvidia driver 550.90.07-5. When I start nvidia with 'nvx on' and plug in an HDMI cable, my system hangs.
I see several hundreds of thousands of lines in system log:
[drm:__nv_drm_gem_nvkms_memory_prime_get_sg_table [nvidia_drm]] *ERROR* [nvidia-drm] [GPU ID 0x00000100] Cannot create sg_table for NvKmsKapiMemory