Sorry, I'll try to make a note on the interview start page about special characters in names. We reached out to the people who provide the tax system about this issue and they said that the IRS's system does not allow non-ASCII characters when doing a digital submission. Your best bet is to use the closest character as possible. It's most important that your tax identification number is correct.
Viewing post in Issues with Tax Interview
The hint about special characters should help a lot. What would also be a great addition is if they highlight the field in which they encounter an error. That way I would have known it was about my name and not the email address.
By the way how long does it usually take after doing the interview that I see the result in my itch.io profile?