Apps that let users create an account must also let them delete that account from within the app — not just by emailing support. Apple checks for this explicitly during review.
In practice this almost always means: no delete option in Settings, a delete option that only deactivates instead of deletes, or a privacy policy that never mentions deletion at all.
"Your app supports account creation but doesn't appear to include an option to initiate account deletion. Apps that support account creation must also offer account deletion..."