I'm assuming you were referring to the animated transition to and from HDR for outputs without a dedicated HDR mode.
That and another problem specifically with HDR screens, but that one turned out to be irrelevant since then.
Imho it would be prudent never to rely on hardware brightness controls being accessible for KWin, and to treat breakage in that case as a bug.
It doesn't, but it relies on brightness devices that are there to actually work. This MR makes powerdevil still advertise the devices but then ignore KWin's brightness values, there's no way for that not to break.
As in, how much value do people get from a temporary reprieve against KWin brightness ownership vs. avoiding inconsistent back-and-forth? I'm kind of tempted not to merge this MR at all at this point
I think that most people that set a non-default brightness with their display's OSD have found the brightness slider or the env var to disable this themselves. So yeah, let's play it safe for the last bugfix release of the series and just wait it out.