Hi,

is that on a standalone Guix system or on another distribution?

Please try to find a file named "org.freedesktop.PolicyKit1.service" in
/gnu/store and then find a line like the following in it:

Exec=/gnu/store/xfysy3c824m4z8b07sbiangp7i2xfh6s-polkit-0.113/lib/polkit-1/polkitd --no-debug

Then please try to invoke that polkitd manually as root.

Does it also fail?