Ive has this issue preventing me from switching to KDE wayland (single monitor)
The monitor wont stay off
After several days of searching i found the following 2 items that fixed the issue:
A: in system settings > startup and shutdown> background services disable Kscreen 2 this partially solved the issue (on xorg it fixed it)
2: on the monitor itself i found a setting that goes something like “select input = auto” and changed it to the proper HDMI port; solved the issue on wayland.
It appears that the monitor starts scanning its ports once the input is turned off, and that triggers a wakeup event.
Posting this in hopes that it helps someone running KDE on wayland with the amdgpu driver.
It may help with other desktop managers, i only have KDE and XFCE insatalled.