On the other hand if I'm casually browsing twitter or instagram I'll gladly like posts that are interesting and there's no cost because it's recreation time.
Also, maybe this is just because I'm just a forgetful idiot, but on numerous occasions upvoting has proven beneficial to me. I'll be searching for the solution to a problem and I find that I've already upvoted a question which relates to my issue - then if there's an answer I've upvoted, that's probably going to be the best one.
My high priority work questions: mostly no answers, even years later. I wrote a self answer, years later one or zero upvotes.
I ask a question with an example, the only answer "solves" the example and ignores the question, I self answer correctly when I figure it out on my own, years later no upvotes.
Several questions I arrive from Google are closed without an answer, or duplicate to a completely offtopic question. Or it's an XY question where I still need an answer for X but I don't have the secret question Y.
If you're not actively gaming SO for karma, it can be kind of a wasteland for anything but read only.