With non matching resolutions the video is letter-boxed, input is not, meaning pressing on the screen doesn't match up properly. Verified with the "show touch" visualisation.
A possibly relevant merge request was started @ https://invent.kde.org/plasma/kwin/-/merge_requests/8720
Git commit 39530b81317851cf0d8d081637245676969f1047 by David Edmundson. Committed on 29/04/2026 at 18:57. Pushed by davidedmundson into branch 'master'. input: Map devices to device outputs, not logical An input device is semantically associated with a physical device, no matter the screen replication. This fixes mapping a touchscreen when it is cloning a screen of a different aspect ratio, we want to ignore touch presses on the black bars. M +24 -14 src/backends/libinput/connection.cpp M +9 -8 src/backends/libinput/device.cpp M +4 -3 src/backends/libinput/device.h M +1 -1 src/workspace.cpp M +1 -1 src/workspace.h https://invent.kde.org/plasma/kwin/-/commit/39530b81317851cf0d8d081637245676969f1047
Git commit 3bfc4de04c479b355b641c12e8cdd9bc29d7d0a2 by David Edmundson. Committed on 29/04/2026 at 19:45. Pushed by davidedmundson into branch 'Plasma/6.6'. input: Map devices to device outputs, not logical An input device is semantically associated with a physical device, no matter the screen replication. This fixes mapping a touchscreen when it is cloning a screen of a different aspect ratio, we want to ignore touch presses on the black bars. (cherry picked from commit 39530b81317851cf0d8d081637245676969f1047) Co-authored-by: David Edmundson <kde@davidedmundson.co.uk> M +24 -14 src/backends/libinput/connection.cpp M +9 -8 src/backends/libinput/device.cpp M +4 -3 src/backends/libinput/device.h M +1 -1 src/workspace.cpp M +1 -1 src/workspace.h https://invent.kde.org/plasma/kwin/-/commit/3bfc4de04c479b355b641c12e8cdd9bc29d7d0a2