libavahi-ui-gtk3-0 from home:den_erpel:trixie-backports project

For Debian Unstable run the following:

Keep in mind that the owner of the key may distribute updates, packages and repositories that your system will trust (more information).

echo 'deb http://download.opensuse.org/repositories/home:/den_erpel:/trixie-backports/Debian_Unstable/ /' | sudo tee /etc/apt/sources.list.d/home:den_erpel:trixie-backports.list
curl -fsSL https://download.opensuse.org/repositories/home:den_erpel:trixie-backports/Debian_Unstable/Release.key | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/home_den_erpel_trixie-backports.gpg > /dev/null
sudo apt update
sudo apt install libavahi-ui-gtk3-0