I’m using Manjaro KDE for 10 years - the same install!!! This is how stable it can be. Of course, some issues came along, but either I or the upstream fixed it. It also depends on how well are you familiar with Plasma and can you fix issues?
Many of KDE issues comes from broken configs so sometimes deleting old ones is needed (like during update from Plasma 5 to 6).
Some people have weird problems, but those are individual ones, so I can’t tell if it works as stable for you as it worked for me. I run Plasma since 5.3 times continuously on the same distro.
Currently, I’m mostly on testing branch, occasionally jumping into unstable branch to get the newest Plasma quicker. No regrets.