Getting music onto my iPhone 14 via Windows 10 laptop using iTunes 12.13.2.3

Since updating my iTunes what, three years ago (maybe 2?), I can't seem to get new music to load into my iPhone 14. Besides having a broad range of interests in musical genres, I am also a composer/arranger, so I have original tunes that I want to load. That, and I still prefer to have the physical recording, as when I sometimes have to go away from a signal or wi-fi, I can't listen to downloaded tunes anyway!

So why in thunder can't I get my phone and PC to play together? I can sync the phone, back up the phone, the "allow to sync" command prompts show correctly on both devices -- everything except to load my music!!!

One other note: I think I back-tracked my iTunes version, as the newest update is when it stopped allowing me to upload. Isn't the newest one like iTunes 17 or something?