Apple ID Password is also no working on that app
I'm hijacking this thread, I have the same issue as the OP. I used the hide my email to sign up on an app that i need to sign onto their webpage but I don't know the password that was set up using the sign in with apple option.
I've hit the link to reset password on the website with the apple relay address, but it doesn't seem to be forwarding to my forward address.