E.g.:
https://sh.itjust.works/u/testaccount789
https://lemmy.ml/u/[email protected]
I know in past I’ve successfully updated my display name, and it shows on other instances, so perhaps this problem is new to 0.19.x, but I am not at all sure about that.
User and community profiles are updated at most every 24 hours so you probably have to wait longer.
Sorry, my mistake.