I was getting the same error when launching grub-customizer in ubuntu 18.04, what I did was just find the path of the missing library:
$ sudo find / -name "libatkmm-1.6.so.1"
/snap/gnome-system-monitor/36/usr/lib/x86_64-linux-gnu/libatkmm-1.6.so.1
after that, I included the lib directory to the file that configures the libs environment variable:
$ sudo su
# echo "/snap/gnome-system-monitor/36/usr/lib/x86_64-linux-gnu" >> /etc/ld.so.conf.d/x86_64-linux-gnu.conf
# ldconfig
and it worked.
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OR you can create symbolic links into an already default lib path:
sudo ln -s /snap/gnome-system-monitor/36/usr/lib/x86_64-linux-gnu/libatkmm-1.6.so.1.1.0 /usr/lib/x86_64-linux-gnu/libatkmm-1.6.so.1
sudo ln -s /snap/gnome-system-monitor/36/usr/lib/x86_64-linux-gnu/libpangomm-1.4.so.1.0.30 /usr/lib/x86_64-linux-gnu/libpangomm-1.4.so.1
sudo ln -s /snap/gnome-system-monitor/36/usr/lib/x86_64-linux-gnu/libglibmm-2.4.so.1.3.0 /usr/lib/x86_64-linux-gnu/libglibmm-2.4.so.1
sudo ln -s /snap/gnome-system-monitor/36/usr/lib/x86_64-linux-gnu/libcairomm-1.0.so.1.4.0 /usr/lib/x86_64-linux-gnu/libcairomm-1.0.so.1
sudo ln -s /snap/gnome-system-monitor/36/usr/lib/x86_64-linux-gnu/libsigc-2.0.so.0.0.0 /usr/lib/x86_64-linux-gnu/libsigc-2.0.so.0
sudo ln -s /snap/gnome-system-monitor/36/usr/lib/x86_64-linux-gnu/libgiomm-2.4.so.1.3.0 /usr/lib/x86_64-linux-gnu/libgiomm-2.4.so.1