Multi-Signature – Is there an idiomatic way to prove ownership of a (extended) public key?

(Extended) Is there an idiomatic way to verify ownership of a public key? While it would be preferable to not use coins, I’m also interested in a way to do so by creating transactions, as this seems simpler.

To provide some context, others may also publicly announce their (extended) public keys for inclusion in the descriptor multi-signature. It will provide peace of mind for everyone involved if everyone who claims to own the key can be proven to do so.