snap list:

Name                  Version         Rev   Tracking  Publisher   Notes
core                  16-2.36.3       6130  stable    canonical✓  core
gnome-3-26-1604       3.26.0          74    stable/…  canonical✓  -
gnome-calculator      3.30.1          260   stable/…  canonical✓  -
gnome-characters      3.30.0          139   stable/…  canonical✓  -
gnome-logs            3.30.0          45    stable/…  canonical✓  -
gnome-system-monitor  3.30.0          57    stable/…  canonical✓  -
gtk-common-themes     0.1-4-g88bc1b2  818   stable/…  canonical✓  -
phpstorm              2018.3.1        74    stable    jetbrains✓  classic
skype                 8.34.0.78       66    stable    skype✓      classic
slack                 3.3.3           9     stable    slack✓      classic

/var not root-owned 1000:0

snap remove gnome-system-monitor
sudo apt install gnome-system-monitor