That's not accurate, sorry. I suspect you're thinking of EIP 2981, which is a standard for universal royalties (and would be about the only way to do what you're suggesting). That said, even 2981 is optional. OpenSea and Blur would not necessarily need to adopt it. They may agree to, of course, which would be good. But then some third-party player could emerge and not enforce royalties. My previous article on this (linked to in the 1st paragraph) explains more why/how royalties are technically voluntary by nature.