I’ve got an additional piece of information regarding external monitor on hybrid laptop. I’ve enabled DRM debugging following Wlroots Wiki, and when trying to enable the external HDMI monitor I get:
[drm:nv_drm_gem_export_nvkms_memory_ioctl [nvidia_drm]] *ERROR* [nvidia-drm] [GPU ID 0x00000100] Failed to lookup NVKMS gem object for export: 0x00000001
Hopefully somebody can shed some light on what that means, in the meanwhile I’ll keep investigating.