Remote identity proofing, either automated to confirm liveness or with a video call. Takes about 3-5 minutes in my experience.

https://help.id.me/hc/en-us/articles/8214940302999-Internal-...

Embassies are supposed to be helpful for this matter. I spent a few years abroad and needed to file ITIN paperwork for spouse and we went in together to get a certified photocopy of their passport for about $50. The IRS accepted this as binding as an American document.

That said, the IRS doesn't really want you on their sites if you don't have a US address. I struggled to get transcripts on the site (but they allow you to submit written requests for them). This is a reasonable thing for the IRS to implement given the significant interest in fraud from their systems from people overseas.

>the IRS doesn't really want you on their sites if you don't have a US address. ... This is a reasonable thing for the IRS to implement given the significant interest in fraud from their systems from people overseas.

Except that US tax law also requires that all US persons, worldwide, to file US tax returns (note: this is a superset of US citizens).

So if the law applies to expats and to anyone who has ever applied for a green card even if denied or not used or not revoked, then the system needs to support worldwide access.

For returns, you can send in a paper copy. That happens to serve as nice proof that you aren’t a resident of specific state for tax purposes

The current IRS online account system with ID.me does allow signing up with foreign addresses, and then you can download transcripts there.

Your struggles were probably with the previous system, which only allowed creating an account with a US address. It did however allow placing an online request without an account for a transcript to be mailed to a foreign address. I did this successfully myself and received the mail in Canada.