They're not requiring just unsubscribe links. They're specifically requiring "one-click" unsubscribe links that can accept a POST request for unsubscribing. This allows their software to have an unsubscribe button that doesn't require the user to leave their software.
This is the RFC that has to be complied with:
https://datatracker.ietf.org/doc/html/rfc8058
Note, that this is not easy for many people using legacy software. It's a major change. I wouldn't be surprised if this requirement gets delayed multiple times.