iPhone won't show up in Music via USB
I sync music files from my Macbook Air to my iPhone via USB. Normally my iPhone shows up in Music (previously iTunes) on my computer as soon as I plug it in, but now it doesn't show up there and I can't sync my music library.
I've tried restarting both my phone and my laptop.
I've tried multiple USB cables. They both seem to work, because every time I plug the iPhone in, it makes the sound to let me know it's charging. Also, the iPhone shows up as connected in System Information under USB, so my computer definitely knows it's there.
I've tried "Reset Location & Privacy" on my iPhone to see if I can get the dialogue that sometimes pops up asking to trust my computer to come up again, but that didn't work.
I updated my phone (iPhone 7) to the latest, iOS 13.4. I updated my laptop (MacBook Air, Retina, 13 inch, 2018) to the latest, Mac OS Catalina Version 10.15.4, which also updated Music to Version 1.0.4.104.
What else should I try?
iPhone 7, iOS 13