Proof of Bitcoin address ownership

Question.

Say two actors have a private key to a bunch of Bitcoin. One removes the
Bitcoin, the other claims it was their Bitcoin.

Given a Bitcoin address is effectively data, how does anyone own it?

are there some sort of data laws that provides the means to "own" the
private key? Or the address?

I'm fairly sure people don't own their biometric signatures, so how could
they own a Bitcoin if they couldn't own their address?