Sometimes I have something nice that I wish to publish, and get some feedback or comments about it from the community.
So should I not post it here? Or maybe there is some other platform for this kind of posts?
Yes, this platform is for reasonably scoped mathematical questions (and answers to them), only.
Questions seeking feedback on material prior to publication are in general not on-topic; typically, they will be "too broad" or they will be "seeking personal advice," two among the reasons for closing a question.
If you have a specific mathematical question related to your unpublished work, which can be stated in a rather self-contained way in a few paragraphs, then it is in principle on-topic.
If you have a specific question about the process of publication, then it is in principle on-topic on the SE site Academia.