@jeffalo did a phenomenal job on username changing functionality - if you change usernames it also replaces mentions all over the site. Absolutely genius!
Or if “what“ username was made in 2020 and he renames to “what??“ in 2022. If in 2023(ik its future lol), someone else registers that username, then
All posts made between 2020 and 2023 mentioning @what will redirect to “what??“
Posts made after 2023 mentioning “what“ (now the new user) won’t redirect