The problem with these approaches is that no significant company is going to do this voluntarily. And this is not going to make a dent until Meta, Apple and friends do it. They are not going to do it because it doesn't give them an advantage, it only makes their lifes harder. It makes it harder even if they don't use the data for anything, because of increased technical complexity etc.
So, this is not a technology problem, but a legal/political problem. Just as the EU is forcing big messaging apps to ensure interoperability now, the only thing that will make a difference here is a law that disallows companies from saving customer data in their own databases. A GDPR 2.0. If you want to make a difference in this space, you need to spend your time pushing new legislation.
I'm sure that in time the EU will get there. And then we will need good tech like Schluss or Solid. But before then, it's not going to do anything.