SUMMARY Blur on transparent backgrounds doesn't work. STEPS TO REPRODUCE 1. Select a background with blur. (Sweet, for example; or manually edit one.) 2. Apply. 3. OBSERVED RESULT No blur. EXPECTED RESULT Blur. SOFTWARE/OS VERSIONS Windows: macOS: Linux/KDE Plasma: (available in About System) KDE Plasma Version: 5.19.4 KDE Frameworks Version: 5.72.0 Qt Version: 5.14.2 ADDITIONAL INFORMATION Have observed the same issue on Manjaro running KDE, and seen confirmed on SO threads.
I can confirm this bug.
*** This bug has been marked as a duplicate of bug 418354 ***