You cannot see the passwords because they don’t exist with Sign In with Apple. It’s a secure token based system so their are no passwords. The app or site developer only ever knows your name, email and a unique secure token that allows them to create the account. That token is not stored anywhere on your device but is linked to your AppleID with Apple. That’s part of the whole point with Sign In with Apple - your account with the app or web site is verified by Apple via your AppleID saying yes, you are you so grant login access. No passwords are stored anywhere on your personal device nor with the person or company offering the app or web site.
If an app or site asks for your account password, you’d either need to disassociate it from Sign In with Apple first and then use your original password. If you made the account using Sign In with Apple, you’d you would have to disassociate it and then recreate it to reset Sign In with Apple.
How to use Sign in with Apple - Apple Support
Manage the apps you use with Sign in with Apple - Apple Support