You only need to provide that to use Primal's built-in wallet, which is provided by Strike.
If you have a Nostr Wallet Connect compatible wallet already, you can link it to Primal in their Android app or on Primal web. This feature is not available on Primal iOS, yet.
Primal iOS wallet settings:
These are both logged into the same npub. So iOS still doesn't have the option to connect a different wallet. Only Android.