I saw this thread, but my issue is slightly different.
I have 2FA turned on for my gmail account, and I’m using an app specific password.
AND… our email appears to be working both in and out.
The only thing with our setup that’s a little odd is that the address we have set up to receive e-mail is support@ourdomain.com, and that forwards to our gmail address, and the gmail is what Discourse polls for new topic creation. And as I said, it’s been working fine, but I’m tired of looking at that issue on our dashboard so hoping someone can help.