Installed guix a few weeks ago on my desktop PC and just yesterday on my laptop (thinkpad L13). Having the same problem on both of them. 

Gnome's default bluetooth "app" doesn't work.

After having the same config as in your example I can launch blueman-manager and connect to my bluetooth sound system. It makes a sound as if it's connected and displays itself as connected but I can't pick it as an output device in gnome's setting "sound" tab.

How have you dealt with this?

(nonnative in english, sorry for possible mistakes)