What you also want to do is pour vinegar down the tube in the tank that water sprays into
That feeds into the "jets" the water gets into the bowl from. Overtime those ports will crystalize over and it's a huge hassle. flushing with vinegar that way will break it up before it fully clogs. And if some are clogged, the vinegar just soaks in there till the next flush
Just the flap and the gasket it seats into, wipe it down with a wet paper towel, see if it still does it
You can also try adjusting the linkage (chain length) sometimes a flap "floats down" slowly because there's still some water. And that might be causing issues.
Anytime you fuck with a toilet, you want to try the least invasive methods first and work your way up.
Shit can get out of hand quickly and you may end up replacing everything and still experiencing the same issue.
You might want to say which part of the planet you're in. Americans just assume everyone has the same medieval plumbing they do, but the vast majority of people don't