First, some specifics for the behaviours you ask about:
Like voting, accepting an answer is completely up to the individual user. Just like there is no "wrong" way to vote on a post, there is no wrong way in accepting or not accepting an answer. The accept mark is really only saying "the asker found this answer the most helpful". They can do with it as they please, there is nothing problematic about this.
Similarily, if you have pointed out a possible improvement on a post and the author refuses to incorporate it, just move on - you have done everything you could. Refusing to accept another user's opinion about the quality of one's post is not problematic in itself, and users are not required to respond to feedback. If this devalues the post significantly in your eyes, you should consider downvoting it.
Comments are for requesting clarification of the post being commented on, or for criticizing it. If comments contain questions that could be asked as questions on their own, you should direct users making such comments to ask a separate question. If they don't and you feel they're asking too many questions in comments, remember that you are not required to respond. If the questions are not connected to the post, you might flag the comments as no longer needed.
And now for some general comments:
Remember that while questions are asked by specific people, you as an answerer are not beholden to them. If OP doesn't like your answer, maybe other members of the community will. You seem frustrated because the expectations of one specific asker seem unreasonable or otherwise annoying to you. But you can simply refuse to engage in trying to satisfy these - from your viewpoint unreasonable - expectations and let your answer stand as it is.
If the question is interesting and you already think your answer might be useful to others, then before trying to moderate away benign variations in how people use this site, maybe you could already be content with that and move on.
On the other hand, if you consider the behaviour of specific users objectively unacceptable (such as violating the Code of Conduct) and not just annoying to you personally, then please also feel free to raise a custom moderator flag on specific instances of such behaviour. If we ultimately find the behaviour not actionable, there's no harm done.