I am not sure if you intended this topic to be answered by anyone else than a moderator/staff member, so feel free to ignore me if that is the case.
I tried to look at your situation from various potential angles, but no matter how you look at it - and reading the rest of your post, I believe it simply comes down to this: You are really giving this too much care for reasons you cannot completely avoid anyway.
And I am not writing this to make your issue seem less important. Believe me, I understand why one would think about stuff like this the way you do. But it still always comes back to the fact that it is just overdoing it without any reasonable benefit. Something that one has to accept at some point.
To get into your points:
About the user: I do not think that they are a bot or are using AI. They are either very young and/or believe writing anything to leave a note/support the creator is a valid use of the comment function. And if you ignore all else - they are actually correct.
Looking through their other comments on their profile page makes it obvious that they intend to write such short comments, either after playing or by just looking at the screenshots of a page. The only thing that makes me go more into 'troll' direction would be specifically the comment about the 'jumping mechanic' - because it is written quite... on the nose, to say the least. But as you wrote yourself, this could also have a logical reason. The thing once more however is: You have multiple reasons, and you cannot pin it down. Not even the staff can confirm for sure that it might be an age thing - at least I cannot remember that you actively have to put your birth date or age when creating your account.
Which brings us to the point of: How far can/should you go as a page creator/moderator? It is your home base so to speak. So potentially, you could moderate the 'intention' of how your comment section should work. But going from what I wrote above about how the user may see the comment section: Are they wrong? Can you make the justified choice to kick them out? Would that go against any fair use of your moderation rights (Which should be a thing in the Guidelines, I would assume).
And that brings us to the final part: All that effort for the following train of thought: How will this user make my comment section look and what image will it reflect to the other users? The thing is you are asking this question in an open web space, where not everyone has the same point of view on things and features, and are thinking about limiting the 'behaviour' as outlined above. The questions here are: Is it really worth it, all things considered? Where are the limits? Where do you have to stop anyway? Is it really that bad to open yourself up to just let it be?
These are questions you have to ask yourself, because nobody else can really give you a final answer to this. You can see a valid reasoning for acting upon this a specific way - there may be merit in there. But it may also be just unnecessary waste of your own energy. Think about it.
On another note: The way you explain your situation and want to resolve it is clashing a bit with what you are actively doing with that mentioned user here. You are writing yourself that you may not want to go all out on them because there could be valid reason for their behaviour and you do not want to be rude. But at the same moment you are openly putting them in a spot light in the global itch.io discussion board. I am not saying you should not have opened this topic. And looking the user up made it possible for me to take my own point of view. But considering: Is it worth it? Are you not thinking too much about it? And during that process: Are you not making a bit overly questionable decisions yourself, even if with reason?
About the locked topic: I read through it (even twice I believe) and I was under the impression that it resolved the issue as much as possible. The points arising here are - as you pointed out yourself - that the system might not be perfect. Especially by just going by the guidelines, I actually had to look up other people asking how the process works and what you can do with it.
But that is exactly the thing: The system works how it does. And in that regard, I believe the moderator gave you all the answers they could have given you - and pinned it specifically because others may want to know it themselves. They locked it because it seemed sufficently done to them and did something that is just common procedure. Asking for more after this is once again thinking into it too much: You are asking for a specific treatment that no one could always foresee being necessary - which is the slight difference to 'actual needing improvement'. I am not saying that they could not improve there either - I think the most obvious problem here compared to other discussion boards is the lack of a private message function - which has been ommited for a reason, however. Everything else you pointed out is - again - quite specific. I for once would not see a reason for why I would need to be notified when a topic of mine gets pinned. And if I would really want to add something to a locked topic, then I read the room: Should I make a new topic? Was it closed by a moderator with the intention of not being discussed any further? Will the moderator eat me (potentially unjustified) if I personally have more questions regarding the closed topic? In regards to your issue - especially after two years - I think nobody would have said anything to you for making a new topic to discuss this further. In some discussion boards a moderator can even merge such topics with the old one.
And if you really think a system needs improvement, they have a dedicated section here to post it. But I would assume adding some more notification check-boxes for forum activity might not have the highest priority for them at the moment.
Again, this is all just my opinion, and I am not perfect either. So take it for what it is worth.
Edit: Having read redonihunter's comment: Something I actually forgot to mention here, is that yes of course: It could also still be something unnatural. Even though (and as they pointed out themself at the end) I believe this not to be the case here.
So it is still a thing you have to judge for yourself. If you have enough reason to believe they are a bot or doing something malicious, it is your very right to ban or report them. But as it is now, and as (including you) three people now have the same opinion of 'Might be, but potentially not' - it just comes back to a user writing comments. Which is just what it is. And honestly: Even if you could ban/report one bot and stop their masterplan of creating good ratings and reviews - as long as it does not go overboard - how much energy do you really want to spend into streamlining your comments and thinking about every spammer/bot/mastermind?