As a counterpoint to this, I've had the KDE DE running for myself (8+ hours a day), my wife, and my grandparents, running on arch for more than 3 years. We've encountered no serious or really even minor bugs in that time. My only active issue is where notifications popping up when using the official Nvidia driver causes render lag for a second.

There was one bug in a KDE application, KDE connect, where it would crash when loading contacts from the phone. But it's open source, so I just fixed it, https://tkte.ch/articles/2021/09/06/KDE-Connect.html.

I'm not disagreeing with the parent post. I'm sure they've encountered lots of bugs. I'm just trying to show that your milage may vary, and for many users KDE just works.