There are some. Not a lot, but I’ve seen a few sign-ups each month that use Unicode characters since we introduced Unicode usernames and group names in 2019.
It was enabled for testing and dogfooding, and I guess we can’t disable it anymore unless we rename all users who have Unicode characters in their username. Otherwise, those users would be broken.
From a technical standpoint, they are… you just aren’t used to typing those letters. 