I was doing a little dig into ballot harvesting and found this resource, Details ballot collection laws in each State.
I didn't see anything about this so if it's a duplicate, I apologize.
As of 2019:[1][2]
24 states and D.C. permitted someone chosen by the voter to return mail ballots on their behalf in most cases
12 states specified who may return ballots (i.e., household members, caregivers, and/or family members) in most cases
1 state explicitly allowed only the voter to return their ballot
13 states did not specify whether someone may return another's ballot
https://ballotpedia.org/Mail_ballot_collection_and_return_laws_by_state