I tried it out for a while and I think a new feature? is that you can control de brightness of the monitor through Plasma. Cool for one monitor but I have 2 and one is brighter than the other at a given brightness %, so it got a bit annoying. I didn't look further into it but when 6.1 is released on Fedora I will probably need to.
Additionally the SDR colors when HDR is turned on looked better overall. Better than Windows was able to do even. Awesome stuff
Plasma 6.1 Beta Review, Its Perfect. ( www.youtube.com )