Same issue for me. gnome-font-viewer froze after launching, either by using Fonts app or command line.
The fix by Luis (mantelitos) in post #14 above works for me. Except one small tweak, remove the space before the "="
$ gnome-font-viewer --gdk-debug=
Once it had launched that way it now launches using the regular Fonts app and plain command line ways too.
Same issue for me. gnome-font-viewer froze after launching, either by using Fonts app or command line.
The fix by Luis (mantelitos) in post #14 above works for me. Except one small tweak, remove the space before the "="
$ gnome-font-viewer --gdk-debug=
Once it had launched that way it now launches using the regular Fonts app and plain command line ways too.
Thanks for posting your workaround Luis.
Ubuntu 20.04 LTS
GNOME Fonts 3.34.0