This is already solved by existing crypto wallet tooling too, you can create an infinite number of keys all derived from a single root key (usually a 12-20 word

This is already solved by existing crypto wallet tooling too, you can create an infinite number of keys all derived from a single root key (usually a 12-20 word phrase in modern wallets). A service with access to a single child public or even private key can't tie them to the sibling keys.