systemd version the issue has been seen with

systemd 251.1

Used distribution

Arch Linux

Linux kernel version used (uname -a)

5.17.9-zen1-1

CPU architecture issue was seen on

x86-64

Expected behaviour you didn't see

When an external monitor is connected to a discrete GPU, KDE's Kwin should be able to access the discrete GPU to connect to the monitor.

Unexpected behaviour you saw

Kwin fails to access the discrete GPU giving the error "Permission Denied".

Steps to reproduce the problem

1. Connect an external monitor to a laptop, with a dGPU which is in sleep state.
2. The monitor is not detected in KDE Plasma in Wayland session.
3. Kwin gives an error saying "Failed to open /dev/dri/card0 (Permission Denied)".

Additional program output to the terminal or log subsystem illustrating the issue

kwin_core: Failed to open /dev/dri/card0 device (Permission denied)  
kwin_wayland_drm: failed to open drm device at "/dev/dri/card0"

Related bug report
https://bugs.kde.org/show_bug.cgi?id=454433