There are of course some people who'll point you to a blog post saying no validation is possible.

However, for every 1 user you get whose full legal name is bob@example.com you'll get 100 users who put their e-mail into the name field by accident

And for every 1 user who wants to be called e.e. cummings you'll get 100 who just didn't reach for the shift key and who actually prefer E.E. Cummings. But you'll also get 100 McCarthys and O'Connors and al-Rahmans who don't need their "wrong" capitalisation "fixed" thank you very much.

Certainly, I think you can quite reasonably say a name should be comprised of between 2 and 75 characters, with no newlines, nulls, emojis, leading or trailing spaces, invalid unicode code points, or angle brackets.