Apparently, it doesn't support 2FA (yet). From https://discuss.privacyguides.net/t/mox-modern-full-featured...:

> Another is 2FA. It would be relatively easy to implement in the web interfaces, but not with SMTP (submission) and IMAP. Most clients can at most do cram-md5 for authentication mechanism (old). I don’t know any clients doing the safer scram-sha-256-plus properly (with mutual verification and TLS channel binding, mox implements it). Interested in hearing what the thoughts are on these topics.