iPadOS 18 and later have moved your saved Passwords from being accessed via device Settings to the new Passwords App. This change improves both access and management of your Passwords and other account credentials - such as Passkeys (new) and 2FA authentication codes - and expands integration with third-party authentication manager Apps.
This fundamental change within iOS/iPadOS is irreversible.

If you only see a blank page when you open the Passwords App, assuming that the Passwords App has been added to the Dock...
With the Passwords App open to the blank page, swipe upwards from the bottom of the screen to expose the Dock - tap the Password App icon - then tap New Window. This should open another Passwords App window showing your stored Passwords.
This a minor bug sometimes seen when initially accessing the new Passwords App after migration. Once cleared using the method described, the problem is unlikely reoccur.