Desktop effects are disabled on login (but can be restored) if the Background Contrast effect is disabled STEPS TO REPRODUCE 1. In system settings, disable Workspace Behaviour->Desktop Effects->Background Contrast 2. Logout (reboot), Log in OBSERVED RESULT Desktop Effects are disabled. Notification explains that they have been "disabled by an app". They can be re-enabled using ALT-Shift-F12. EXPECTED RESULT Desktop Effects remain enabled SOFTWARE/OS VERSIONS Windows: macOS: Linux/KDE Plasma: Arch / 5.12.10-zen (available in About System) KDE Plasma Version: 5.22.1 KDE Frameworks Version: 5.83.0 Qt Version: 5.15.2 ADDITIONAL INFORMATION NB., this is under X11 with compositor set to OpenGL 3.1. Most other options are default or near-default (Breeze Dark theme).
Cannot reproduce.
On further investigation, this only occured when I had an external monitor attached to my laptop (intel graphics, i915). In a live plasma session, adding _or_ removing the external monitor reliably suspends desktop effects, but _only_ if Background Contrast is disabled. Apologies for the misreport earlier.
This bug was reported against an outdated version of KWin. We have made many changes since the. If the issue persists in newer versions can you reopen the bug report updating the version number.