What you're referring to is a source of entropy.
You could use a Bitcoin wallet's private key to generate entropy for a new npub through a new wallet address (public key) and if implemented correctly it should be possible to cryptographically prove with a very high level of probability (virtually impossible to fake, would take millions of years to brute force) that the two are connected.
The input would have to be the wallet private key because if it was derived only from a wallet address, since that's public anyone could generate an npub from one.