Created attachment 106463 [details] Scrolling using the mouse wheel is only possible if the cursor is inside the window When you maximize a window with a scrollable content, you can't scroll anymore using the mouse wheel / touchpad gesture when the cursor is at the most left position of the screen. The scrollable content of the window has to reach to the border of the window (like it is in Firefox, konqueror, konsole, ...). It sound's a bit strange but it is very bad for UX if you're used to the behavior that you can always scroll in a maximized window even if the cursor is at the margin or the screen. This may only be the outcome of an other change of kwins behavior.
as a workaround disable the touch screen border. On Wayland this issue does not exist. I mark the bug as wontfix as we got similar bug reports for it, but it's not a simple fix. Either we support touch screen borders and have this bug or we don't support them and don't have this bug. Anything more sophisticated would require a larger change in how this code works and that won't happen for a bug fix release.
Thanks for figuring out the cause of the issue. I'm not sure but I think I also had to disable active screen corners and edges. I can understand that decision and it works for me.