Itch.io appears to have updated its OAuth API, but Epic Online Services (EOS) does not seem to have adapted to the changes yet.
As a result, attempting to log into the game using an Itch.io account now triggers an EOS server exception error.
This will require a server side change of EOS to fix the issue. Any game that uses EOS to auth with Itch.io is now broken.
I reported to InnerSloth (Among Us developer and their game uses EOS and they are doing nothing) and EOS community support (their team is trash and is doing nothing) and they don't actually care. This is a common issue that has existed for more than 3 days and nobody cared. I assume posting it here can draw your team's attention(since you should be able to get in touch with the big busy people in EOS)?