Since 5.13 mouse settings have been minimized. It is, for example, no longer possible to set the amount of lines the contents of a window scrolls with one mouse-wheel notch. It is by default set to 3 which is way too many. In Dolphin, in icon vuew, the complete contents of a directory is scrolled of screen by one simple notch. Unworkable. Please restore the old settings. Thank you.
This is because we finally implemented a GUI to controls mice when Libinput is used as the backend. Unfortunately, libinput doesn't provide this feature. If you would like to keep using it, you will need to remove libinput and use the older evdev driver for your mouse, which still has the feature.