Is it allowed to create users with special characters in the name?

An idiot user has shared a folder creating a guest user…but has added a “,” in the name, example “I am a guest user, and I want to use nextcloud” now I can’t list it to delete it, it appears now as a guest but I can’t share anything, if I look for it with occ user:list it doesn’t appear either but in the web it does.

Here is the link to the central issue on Github on this topic: