That’s right. If you want to use a service and continue to use the service, it’s your responsibility to know what email address you used. If you forget, then you have to create a new account. The alternatives are all much worse. Email the admin (who does not publish their email address, so you’ll need to create a new account to contact them), then say “Uh, I created an account with an email address that I don’t know. I can’t prove I own it, since I don’t know what it is.” Or you could ask “I created a username secret123, I forgot what email address I used, can you tell me?”
If you’re paranoid enough to use random email addresses then you’re paranoid enough that you use a password manager that will remember the info for you, otherwise, you’re out of luck.