After 13.5 years of using Discourse, I never realized this.
The same list can be obtained by sorting the Active users list on the Created column (/admin/users/list/active?order=created) so I suggest we get rid of that New tab? It is confusing and redundant, and I expect tabs to filter, not to sort.
Edit if it is removed then there should be a proper way to sort that list on mobile. There currently is not.