The current packaged blueman for 24.04, version 2.3.5-3build1, results in the following error when the Devices panel is opened:
GDBus.Error:org.freedesktop.DBus.Error.InvalidArgs: Unknown action ‘Activate’ (16)
This would be innocuous if not for the resulting Internal error bug-report requests.
I have tested compiling and building blueman myself, and the error does not occur with 2.4.3. Compiling and building from the git source is a bit rough. There is a slightly easier option: build the debian package, e.g.:
First uninstall blueman
sudo apt remove blueman
Then install dependencies, clone the repository using Git, build the debian package, and install via dpkg:
sudo apt install git python3-dev libcairo2-dev libgirepository-1.0-dev python-gi-dev cython3 libbluetooth-dev debhelper dh-python libpolkit-agent-1-dev
git clone https://salsa.debian.org/debian/blueman.git
cd blueman
dpkg-buildpackage -us -uc -nc
cd ..
sudo dpkg -i blueman_2.4.3-1_amd64.deb
Lastly, restart the systemd service:
systemctl restart --user blueman-applet.service
The Devices panel should now open without generating an error.