@mdm The current vote by mail rules from the #Minnesota Secretary of State's office: https://www.sos.state.mn.us/elections-voting/other-ways-to-vote/vote-early-by-mail/
"Who can witness my ballot?
You will need a witness when you vote and complete your ballot. The witness can be either a registered Minnesota voter or a notary."
I keep complaining about this to my members of the Minnesota state legislature.
(On the other hand, all one needs to get a ballot by mail is to fill out the form online - or by mail or in person in a county election office.)