Win10 fully updated. That was required before iTunes or Apple Devices would even recognize my new iPhone 15 Pro Max. Then that didn't even work. My new iPhone had to be updated, then it crashed and I had to factory reset the blasted thing and redo the update, then voila! my pc saw the phone. I was then sent from Apple to the Win store to download iTunes and Apple Devices. That version of iTunes wouldn't even perform the backup function and required the Apple Devices app for that function. iTunes was a shell of a music player at that point and music only. I found a download for a standalone version of iTunes and installed that to transfer my music, then realized it was only uploading to the cloud, then if I wanted my music to be 'permanently' on my phone I had to upload the same music to the phone. Your only other option was streaming every song. If you check Apple support, they tell you that you have to have the Apple Music subscription or you will lose that transfer ability. I don't know yet if you lose access to 'downloaded' files on your phone if your subscription lapses. I also downloaded a 3rd party player app from Apple Store and transferred everything from Apple Music app on my phone to the 3rd party player. It took 3 weeks for this simple file transfer to work. I was on the phone with Apple Support and back & forth with Microsoft Support as well as Verizon (who didn't know crap from shinola) while they blamed each other.
If you have an Apple Music subscription then there is no need to load the music files for songs that are in your personal library to the iPhone...the Apple Music library is vast and Apple Music will stream/download Apple Music copies of the music files you own it finds on your Windows PC to your iPhone from Apple’s servers. If you have no Apple Music subscription it just syncs your personal music files over to the iPhone. For music you have that isn’t available in their Apple Music library it should allow you to copy that over with iTunes for Windows.
https://support.apple.com/guide/itunes/sync-itunes-content-with-your-devices-itns5ecc4d98/windows