3. systemd-logind ships a default set of udev rules that tags any
framebuffer devices (/dev/fb*) as "master-of-seat", which is OK for all
KMS-compliant video drivers like Intel, Nouveau (open-source driver for
NVIDIA graphics devices) and Radeon (open-source driver for AMD graphics
devices).
4. However, NVIDIA or AMD proprietary drivers don't expose kernel
framebuffer devices, so they need their own udev rule to tag another
kernel device they expose as "master-of-seat" (in @elfy example, we tag
kernel device /dev/dri/card0):