SUMMARY With an external monitor attached to a laptop, playing any video full screen causes the video to be duplicated on all monitors. STEPS TO REPRODUCE 1. Plug an external monitor into a laptop using DisplayPort. Configure the displays in "extend" mode. 2. Play a video on the main display using VLC or YouTube on Firefox. (I haven't tested other video players.) 3. Instruct the video to play full screen. OBSERVED RESULT The video plays full screen duplicated on both the main and external displays. The copy of the video playing on the external monitor does not observe that display's rotation setting, instead playing in 0deg rotation. EXPECTED RESULT The video plays full screen on only the main display, leaving the external display unaffected. SOFTWARE/OS VERSIONS Linux: Kinoite 37.20221203.0 (kernel 6.0.10-300) KDE Plasma Version: 5.26.4 KDE Frameworks Version: 5.100.0 Qt Version: 5.15.7 ADDITIONAL INFORMATION CPU: Intel i7-8550U GPU: Intel UHD 620 Mesa: 22.2.3 Please let me know if I can provide any additional information.
Please check if your monitors are slightly overlapping. KWin assumes they don't, so when that happens, it can cause problems
Sure enough, my displays were overlapping by about one pixel. Fixing that also resolved strange behavior I had previously noticed with maximizing windows on the second monitor. Thank you for your assistance with this.
Great! I'll mark this bug as fixed, as starting at 5.27 such buggy display configurations should be automatically prevented in the display settings