How can I access passwords for "sign in with apple" accounts?

I've used "sign in with apple" to log into several 3rd party services. My understanding is that apple creates a strong password and a private relay e-mail address and remembers both for me... which is great.

The problem is that some of these services require actually typing in your password occasionally. So my question is: how can I see the actual underlying passwords stored for these accounts? I couldn't find them in Keychain...

Specifically, “Sign in with Apple ID” apps ask for a password to deactivate, so what do I type?