Its very difficult to get into. I liken it most to maths, you simply cannot take something written for someone with a certain higher level of understanding than you currently have and expect to get much from it. You simply must go page by page slowly, deliberately, and humbly, taking the time to completely understand each term you come across (which will often require a several hour diversion, in which you come across more terms branching all the way down, etc). You can't skip over terms like "intervals", "locrian/lydian" and hope to understand them by osmosis.
Except, if you are asking how to learn algebra or statistics to a certain level, I could give you a list of certain theory books and exercise books in a certain order (some of them, admittedly, written in an unnecessarily complicated way in my opinion and you would be better off with some youtube videos, and for some of them I really don't know a more approachable (= better) alternative, but I think there could be), and be fairly confident that you at least could follow them and actually achieve what you were asking for.
And there's no single actual music theory book recommendation in this thread.
(And I don't think it's a lack of patience to learn terms that's the problem here, definitely not in my case. I know names for all intervals literally for a longest part of my life. I kinda know how each of them "feels". But it's still too far from being able to write music "algorithmically", and I don't know what would be the next step. Most books I come across just try to teach me interval names once again, and I'm pretty sure there must be more theory in music than that.)
If I have to give my recommendation, I used "Idiot's Guide: Music Composition" by Michael Miller. It required a lot of background reading, but once I understood chords and chord progressions well and melody construction it started, slowly, to come together. I don't know that it's a good book, but it worked for me.
I then read "A first book of blues, for the beginning pianist" by David Dutkanicz, which led me into blues which is kinda its own thing, I couldn't apply some of the algorithmic rules I had learned to the blues scale and I wanted to understand why. Admittedly the book didnt teach me the background theory of why that is the case but I did learn more concepts like syncopation and ways that the blues scales are constructed from a major scale and why
