Toilet handle hard to push all of the sudden?

I had some house guests come, my least favorite thing lol, and realized after they left my once easy to flush toilet now seems like there’s resistance. Have used it for a decade and no issues, and coincidentally it’s super stiff now when pressing the handle. Is there something they could have accidentally done?

I opened tank and didn’t see any issues with flapper or chain, etc. just feels like an initial bit of pressure / resistance when pushing lever I don’t recall ever having.

It was a very tad bit colder out this weekend here, but heat was on and bathroom wasn’t really any much cooler than it’s been in the past on a colder day here.

Anything I can do to make it soft push again? I sprayed some vinegar around the handle and wiped it down, in case some sentiment or something got lodged in?

Not really a big deal, just found it odd that it would happen randomly right when they left.