My passwords have all gone from my ipad

Having updated to iOS/iPadOS 18.x, you will not find your saved Passwords in iPhone or iPad device settings. All saved passwords have been migrated to the new Passwords App which you will find on one of your Home Screens, or from the App Library.

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.

have you checked in passwords App and keychains .

If doesn't found check your iCloud settings whether you might saved/synced your passwords or not .