Seems that system setting "Mouse wheel scrolls by" in "Hardware/Mouse" settings is completely ignored by Dolphin. And by default scrolling moves the icons just by a very tiny amout. Go to to the next full page of icons on full-screened Dolphin (about 5.5 rows of icons) I have to do full 9 scrolls with my finger. Reproducible: Always I have hi-DPI screen, ~2500x1400 px on 14 inches. In previous version scrolling worked fine, albeit I don't know if settings were obeyed or just the default setting was better for my use. Nevertheless, the scrolling setting is still ignored now, hence this bug.
Thanks for the bug report. This issue has been reported a long time ago already, but it seems that it causes more trouble now with high DPI displays *** This bug has been marked as a duplicate of bug 295571 ***