Steps to reproduce the issue

1. In Windows 10 Ensure the option: Settings > Ease of Access > Display > Show animations in Windows. is UNCHECKED
2. Open Joomla 4 site as administrator
3. Try to open/close the drop-down menus in sidebar left

Expected result

Menus open/close/toggle correctly

Actual result

Menus dont open/close/toggle correctly

System information (as much as possible)

Joomla_4.0.0-beta6-dev-Development-Full_Package (nightly build : 2020-11-09) installed with Wamp on Windows 10

Additional comments

Problem appears to be with the recently added
CSS rule : @media (prefers-reduced-motion: reduce) {...} in the administrator atum template CSS

Comment this out and all works fine again.
I am not clever enough to determine why this css rule does not work or I would submit a patch to github