You have to run something like sudo apt install libgtkmm-3.0-xxx. The xxx must me replaced by a distro specific version string. For Ubuntu 18.04, it is: libgtkmm-3.0-1v5.
You have to run something like sudo apt install libgtkmm-3.0-xxx. The xxx must me replaced by a distro specific version string. For Ubuntu 18.04, it is: libgtkmm-3.0-1v5.