I'm very curious on how 1st party cookies will be used for tracking. How can they connect one website's cookies to another's? All I can think of is fingerprin

I'm very curious on how 1st party cookies will be used for tracking. How can they connect one website's cookies to another's? All I can think of is fingerprinting, but afaik you can't really be sure "who's that" since fingerprinting filters people out, and isn't good enough to target a single individual. I guess they can improve it, but there are ways to work around it too, it will probably be easier to fix fingerprinting than blocking 3rd party cookies. Its seems that if 1st party cookies were as good they would have switched to it by now.