how proper are we talking? "for you"-like?

in that direction - certainly a level above regex-y ones. Like I don't really comprehend how you're supposed to figure out what's relevant, like I could imagine how you'd do it for one specific person but figuring it out on the fly for everyone who might possibly look at your feed? no clue

it's out of my wheelhouse really but iiuc you first want a really big database, then start doing "collaborative filtering"

you probably want to start calculating correlation coefficients between users based on their like/follow histories (you can treat them as really big vectors)

and then you can do "users similar to you liked these posts"