What I showed is taken directly from the arch wiki.
Oh…
I have polkit-gnome installed, and it provides both polkit-gnome-authentication-agent-1.desktop and /usr/lib/polkit-gnome/polkit-gnome-authentication-agent-1 (but it isn’t a systemd service file, it’s a binary).
I think chasing a polkit-gnome-authentication-agent-1 systemd unit isn’t the right way of solving my problem, as I see that my system is capable of providing me with GUI password prompts (e.g. when I try to use the GUI for package management). So that “subsystem” is working and most probably doesn’t need an additional binary running in the background.
So the reason I stopped getting GUI prompts for pamac on the CLI is probably some change in polkit’s settings. I’d just like to know if that change was something intended by the maintainers, or was an accident with the update (like gdm being marked for autoremoval)