This is a really hard lesson to learn and it takes most people (myself included) many tries to learn it. From reading your post, it is super clear that you understand the lesson-- validate your idea early. But understanding the lesson and actually learning it are worlds apart.

You have put a lot of time into this project, and it is not going to go anywhere. This is a tough realization. One that you naturally want to argue against. It's easy to be stubborn. But the more time and effort you put into this, the more time and effort you are wasting.

The positives: you have built a foundation and undoubtedly learned some things along the way. Take that knowledge and pivot to something that people want/need. Good luck!