This was fixed for me since 5.27 but it resurfaced with 6.0. Breeze/Lightly/etc are fine; it's Aurorae themes with fractional scaling in Wayland that have the issue. Not sure whether it's a bug or something left over from somewhere in my system.
I've been helping out with bug triage since Plasma 6 released (I'm not a Plasma developer though, so take whatever I say with a healthy helping of salt). There have been a fair amount of bugs regarding fonts and fractional scaling, and a bunch of them seem to be upstream Qt bugs. So, it's not just you/your system. There seem to be workarounds for some cases, but unfortunately I can't say how long it will take for an out-of-the-box fix.
I sadly, and I don't say this lightly, have to agree.
When first using KDE, I was totally baffled by the amount of themes you can download.
But I quickly learned, that most of them are either more than 5 years old, look ugly/ incoherent, or cause this blurriness issue OP mentioned.
For my taste, Breeze (or to a further extend, Lightly) looks phenomenal by default, especially since Plasma 6. I only change the color scheme a bit (usually just adaptive colors, based on wallpaper), but that's it.
Definitely! The only "good" 3rd-party themes are the ones from Jomada (Edna, Moe, Itchy, etc.) and from Vinceliuice (Graphite, Canta, Layan, etc.).
Those are well thought out, coherent and look professional.
If you scroll through the top ones, then you almost exclusively find ones that got their last update years ago, and now look extremely incoherent or buggy.
And even if you find newer ones, then they often lack the polish.
Man, it just sucks...
But hey, maybe there is just not that much demand anymore, because the defaults look great nowadays?
But it's the second best thing about KDE! My themes are constantly thoroughly fucked around with.
Also, my upgrade to Plasma 6 went borked but I'm sure that's pure coincidence. 🙄
First thing I learned with KDE was to definitely fuck around with the themes, it's one of the great things about it. Was just looking around, seeing nobody else has reported something similar to this, hence I wasn't sure whether it's a 6.0 regression or whether it's something unique to my system. If I wanted a system that others are making the decisions from me, I'd use other DEs (of the garden ornament variety).
Of course that's KDE's strength. But it's also it's greatest weakness, I find.
Since KDE 3 came out, I find that whenever I install a new version of plasma and mess around with the themes, something breaks. And often breaks permanently to a point I have to delete all KDE files in my home directory.
I get what you're saying, I used KDE even back in the 2.x days. I could argue that this is kind of different though; it's not only third party themes, it's everything based on Aurorae. For example, Plastik comes with Plasma by default. Guess what, also has an issue.