SUMMARY *** I have a HiDpi laptop that it seems linux doesnt know that is HiDpi and X seems the dpi as 96. so I have to use global scale @150% zoom. I also use the autohide option of bottom bar. I noticed that some apps (like dolphin) when I maximize them the bottom of screen has a small strip that is not used by the app. I noticed this because my firefox was maximized and dolphin was maximized and I could see some horizontal line form firefox at the bottom of dolphin window. this seems to be occur when the bottom panel is in autohide mode. if I select the "windows can cover" then this doesnt happen. but even if that mode I noticed I can see the blue tint (line) of the app this last selected in taskmanager in panel at the bottom of dolphin. so maybe it is dolphin and and some other app (cant recall them right now) that dont do 100% to the bottom of screen because I cant see that blue color at the bottom of maximized firefox or maximized telegram or brave app. another app that I can reproduce this with is kate, so two plasma apps that I use. See https://community.kde.org/Guidelines_and_HOWTOs/Debugging/How_to_create_useful_crash_reports ***
*** This bug has been marked as a duplicate of bug 391956 ***