Unsurprisingly the answers you get from this board are goign to mostly be shit.
The most 'god-tier' theory book I've read is "A Generative Theory of Tonal Music", assuming you actually want a serious book that theorizes about how the human mind potentially perceives the musical structure of common practice music at a high level, and not a "teach me how to do music stuff" book.
For more 'alternative' theory that traditional methods barely explore, "Tuning Timbre
Spectrum Scale"
https://sethares.engr.wisc.edu/ttss.html has some of the most interesting material on how timbrel qualities of sound can affect how dissonance is perceived in various scales, and builds up a theoretical approach to programmatically derive combinations of sound qualities, tuning and scales that 'work well together'.
