I'm not actively working on th 6815 is extension anymore since I personally switched to PipeWire, however if there are people using it I'll try to keep it updated for new gnome-shell versions and will accept bugfix PRs!
gsjackctl is a simple GNOME extension to control the JACK audio system. It works only with jack2 using jackdbus.
Dev install:
git clone https://github.com/cbix/gsjackctl ~/.local/share/gnome-shell/extensions/gsjackctl@cbix.de
Or get the latest release by downloading the gsjackctl@cbix.de.zip asset from the latest release.