I once wrote a book (about 400 pages, after editing). No one read it, and rightly so. It covered a topic in a preachy, dictatorial manner. It’s long buried in a deep, unmarked grave, in the desert.
It was accurate, well-written, well-structured, relevant, and useful, but assumed a tone that was pure poison. It was aimed at an audience that did not respond well to the tone.
It was extremely valuable education for me, though. My mother was a scientific editor, and edited the book. It was brutal, and quite humbling, but her work ensured that the book was absolutely perfect. I don’t think I’ve ever shipped anything as close to [unpopular] perfection as that book.
Even though I have never been particularly interested in writing book-length stuff, since then, I continue writing to this day[0]. Here’s the latest thing I did (released a few days ago)[1]. I don’t really write for others; I write for myself.
Good luck.
[0] https://littlegreenviper.com/miscellany/
[1] https://littlegreenviper.com/series/passkeys/
[EDITED TO ADD] I typically get some downvotes, when I link to my postings. Long ago, I favorited a comment that I made, explaining this[2]. I don’t expect anyone to actually read it before hitting the down arrow, but I figured that I’d add it here, for elucidation.