When approvers override is disabled at the project level, it should still be possible to remove approvers set in a specific MR

With the new Can override approvers and approvals required per merge request setting disabled:

while a MR already had some approvers explicitly (aka "overidden approvers") set, it's now impossible to remove these approvers:

One solution would be to always allow to remove explicit approvers (by adding a new :remove_approvers rule).

Another solution (from @smcgivern) would be to add a UI element to reset a MR approvals to its Project's default. This element would always be available, even if you can't :update_approvers, as long as you can :update_merge_request.