How to check what are the config changes made by admin access user in LTM 11.5.1

Unfortunately, there's no simple way in BigIP to get a list of differences between the units, though you could generate a qkview on each, upload them both to select them both and click on compare - that would give you a list of all the objects that differ, but it's not a very automated solution.

The best way to rollback would be to create an archive (UCS file) prior to performing the sync, and then restoring it if you needed to revert.