How can I know if I have Gnome or KDE? [duplicate]
(this follows on from comments. @DK Bose provided
env | grep XDG_CURRENT_DESKTOP
which confirmed 'Unity' as the DEsktop)
Unity is a Canonical DEsktop that is a drop-in-replacement for gnome with advantages & of course disadvantages; it isn't gnome but uses the same version of GTK+ /Glib so can use gnome apps without disadvantage (no wasted memory etc)
As to tweaking: instead of trying to use 'gnome-tweak-tools' I suggested adding the Unity Tweak Tool
sudo apt install unity-tweak-tool
as it provides far more options for Unity than gnome-tweak-tool.