I use user edition. After upgrade to 5.9 kwin window decoration (Breeze) disappeared. Upgrade to 5.9.2 didn't helped. I deleted .config/kwinrc but no improvement. What can I do? What more relevant data can I provide?
I purged neon user and installed dev stable and added new user account to be sure that it is not about settings. But the bug still is present. Maybe it has something to do with nvidia in relation to kwin?
Problem solved. I reinstalled dev stable.