I´ve installed a couple blur forks (Better Blur DX and Glass) and initially they worked fine, but today both went missing from the Desktop Effects tab and I can see that Glass (which is what I was actively using) really is no longer enabled. I tried reinstalling the packages (both were installed via dnf repos, this is on Fedora 43 KDE) and re-logging in, but that didn’t help. I think this may have happened after updating from Plasma 6.6.3 to 6.6.4 but I’m not 100% certain. Is there something known in Plasma 6.6.4 that could cause this?
The package needs to be rebuilt against the latest Plasma version, or more specifically to the newest KWin version, granted that it still builds for that version and doesn’t require some changes from the developer first.
from https://github.com/xarblu/kwin-effects-better-blur-dx#installation
If the effect stops working after a system upgrade, you will need to rebuild it or reinstall the package. The effect only works for the exact KWin version it was built for. Additionally KWin needs to be restarted (e.g. via logout+login) to load an updated version of the effect (the initial install doesn’t need this).