Hello Sandro, hello Norbert, this sounds like the feature "Highlight lines coming into view" [1].
There is an option that looks like it could be disabled in: Profiles - Scrollbars - "Highlight the lines coming into view" Kind regards, Bernhard https://invent.kde.org/utilities/konsole/-/commit/dabac1f47ead4626f0ff83affb851309f10a6e58