Now I see what happened. My system was up-to-date. sudo pacman -Syu and yay -Syu told me there were no updates to install. Yet, as you point out, my Python was oudated.
I’m using asdf-vm to install and manage user Python versions. My ~/.tool-versions file said this:
python 3.10.7
I changed it to this (source):
python system 3.10.7
Then I ran yay -Syu protonvpn and it worked. Resolving.