>>1457485Didn't help, unfortunately.
Here's something else I tried:
-Booted PC to UEFI
-Plugged phone in via the C-to-C cable that goes in the back
-Ensured mode was set to file transfer
-Charging light was on
-Booted to Windows. Charging light disappeared.
-Set mode to File transfer (again)
-Noticed there was a notification for "installing software" tap it
-Two things instantly show up in Explorer. One of them was the model number of my phone, the other was presumably some software for Xperia transfer or something
-Charging light is back too
-MTP "folder" is empty
-Disconnect and reconnect
-Back to square one
At this point this is definitely a Windows/driver thing. My last motherboard didn't have this problem. That said, I'll be damned if I'll have to reinstall Windows just for this.
Even more puzzling, if I switch the USB mode to MIDI, then "no data transfer", I get the "install software" popup on my phone. I tap it, and I can see things show up in Explorer. And I can access the phone's storage from Windows! But if I then unplug and replug, I'm back to square one, kinda?