First of all, it’s great that KWin supports VRR as well as it does.
One problem I found with the feature is that when switching from VRR to non-VRR, my screen blanks for about a second. This is slightly annoying when switching out of a full-screen game, but it’s not very tragic.
Where this is really jarring is the region picker of Spectacle (the screenshot tool).
This is coded as a full-screen application, so when I press the “Rectangular Region” button in Spectacle and then select a region, the screen blanks for about a second before I get to see the results.
It would be lovely to be able to “ignore” some full-screen windows when deciding whether to switch to VRR mode. This would also be useful for full-screen YouTube videos for the same reason.