It should come up with only a bit of effort. But if you’re like everyone else and never use the thing the stopper could be stuck. WD40 might help, but I’ve had luck with CLR too (since the mineral deposits can stick it in place. Remember to pull upwards, and make sure you’re not hitting the top of the overflow, since the linkage does tip outward.

This past summer I helped my dad remove the plumbing off a drain and we beat it out with a hammer.. thankfully the drain assembly was still good and we could replace it. Helps to have an unfinished basement sometimes :)