I am in a similar situation with @Noob_Of_All_Trades. Updated the phone yesterday with sudo pacman -Syu, then all sound is lost.
I tried commenting out the quoted section in PinePhone.conf (I am able to do so with sudo), however after a reboot, it still had no sound.
I then restored the original PinePhone.conf and tried to rename ~/.config/pulse. I did not have a ~/.local/state/wireplumber file. After a reboot it did not work either.
Please help.
Edit: I also tried to downgrade all upgraded packages (looked at /var/log/pacman.log and restored the original versions from /var/cache/pacman/pkg/), and also tried to uninstall alsa-ucm-pinephone. Then retried the PinePhone.conf and .config/pulse fixes, but still no luck 
Edit 2: I managed to fix it!
After I downgraded and uninstalled alsa-ucm-pinephone it still didn’t work. So I upgraded again, and then manually reinstalled alsa-ucm-pinephone. Then rebooted, and suddenly I have sound again.
I note that If I look at the alsa PinePhone.conf now, it is significantly shorter. Not only did it not contain the SectionDefaults, but the boot sequence stuff is all gone as well. I suspect that’s probably the cause (?)
@philm Based on your comments here and on the GitLab commit, I suspect that the version with only SectionUseCase."HiFi" and SectionUseCase."Voice Call" is the correct one? In which case, I think your “alpm hook which makes sure to restore the symlink” maybe is not working with pacman -Syu…