As one published author to another, send that dang manuscript out. Give it to betas, give it to an editor, do their feedback and SHIP, dammit.
12 years and 3 complete rewrites – you have to get that out of your way, even if it winds up in the dumpster. It’s never going to be perfect. Ever.
Your personal growth affects how & what you write, and vice versa. Working on one piece this long means you are already a different person than when you started. So you need to be writing a different book. Trying to turn the book you needed then into the book you need to write now is going to keep you frustrated.
You can’t get the growth you need from this book until you declare it finished and move past it. Get other eyes on it and let it go.
It’s terrifying but such relief. Best wishes.