An unregistered person can’t send DMs so that wouldn’t work for problems signing up.
Equally I suspect a person having trouble signing up here wouldn’t bother joining Teams, so that option would only work for somebody that already uses Teams.
Maybe a better idea would be a simple HTML enquiry form that allows a brief message and asks for an email address so you can answer. That tends to be safer then publishing an actual email address, which search engines add to spam lists.
Enquiry forms also tend to attract spambots, but I’ve found it easy to prevent that. Simply add an extra question (with css display:none so real people can’t see it). Spambots work by posting spam into every text field but they’re too thick to check whether the field was displayed — so the posting script can discard any submission that contains the extra answer.