Thought it was worth mentioning: Tumblr and letterboxd accounts both have in-built RSS feeds, so if you'd like to follow some people without using the sites themselves, that would be my recommendation. I use letterboxd this way and really enjoy it - I can get film recs without having to deal with letterboxd & serializd's tendency to shove bad takes from total strangers at me.
I don't disagree with any of the criticisms of Tumblr in this thread - it is, indeed, having a serious problem with racist and transmisogynist moderation at the moment - but I have been using it for a decade and am unreasonably attached to the hellsite. If you do go that route: pretty much all of the algorithm features can be switched off in settings; Xkit Rewritten is a godsend; make liberal use of the block button.
Re. finding new interests, it really just comes down to finding people whose opinions you trust, no matter what form that takes. I have a Tumblr mutual with incredibly good taste in TV shows; if they start blogging about something, I know to give it a try. I have friends who buy me books for Christmas. Critics are also great for filling this role - I get most of my horror film recs from Sarah Zedig's YouTube videos. Go beyond 'are we into the same media?' and into 'what are my thematic/aesthetic/political priorities for what I consume? how far are we on the same page?'. This is, in my opinion, worth doing just for the sake of clarifying why it is you like the things you like - but it has the added bonus of making it much easier to seek out new interests.