Username should be using ASCII only

It seems the allowed characters for usernames of Minecraft Java Edition have changed. Up until recently a username could be validated by using a regex like "[a-zA-Z0-9_]{1,16}". Now at least
"ſ" (U+017F) is used, too.

For reference: https://de.namemc.com/profile/calledſnipes.1

Is this an mistake?
If it's working as intended, please provide a documentation of all allowed characters in user names.