In Plasma 5.22, the shadow of the Kickoff and the taskbar has been updated. However, they have a visible "stop", in other others, they aren't gradient enough like in previous versions of the Breeze plasma theme. The shadow might look better if it were more gradient.
Seems like this would be fixed by https://invent.kde.org/frameworks/plasma-framework/-/merge_requests/270.
Done in Frameworks 5.86 by Niccolò Venerandi with https://invent.kde.org/frameworks/plasma-framework/-/commit/c9d29028ca358e8c0a8f9d47c5e7f69594f78a34!