When "Synchronize group memberships when logging in" is set to "Every time a user logs in" the "last updated time" user attribute updates every time a user logs in.

Once "Synchronize group memberships when logging in" is set to "For newly added users only" the attribute no longer updates.

Many teams use the "last updated time" user attribute for internal tracking purposes. It would be helpful for the attribute to still update with "For newly added users only" as many teams use the "For newly added users only" setting for performance purposes.