Worked until 5.25.2. When I switch from folder layout to workspace layout (don’t know the English version), the workspace switching via mouse wheel does work again.
KDE Plasma Version: 5.25.2
KDE Frameworks Version: 5.95.0
Qt Version: 5.15.5
*** This bug has been marked as a duplicate of bug 419867 ***
*** This bug has been marked as a duplicate of bug 419878 ***