Cinnamon was a reaction to GNOME 3. But Cinnamon was written from scratch to reflect a more traditional desktop metaphor. It was not created from existing GNOME code.

In the days of GTK 3, Cinnamon shipped quite a few of the default GNOME apps. Later, when GTK4/ libadwaita appeared, Cinnamon stayed with GTK3 and formed the XApps project which did fork many GNOME apps to stay on GTK3. XApps was meant to be a cross-desktop project serving all the GTK desktop environments.

These days, Cinnamon is trying to fork libadwaita to make GTK4 apps look better on their desktop.

In general, Cinnamon is fairly conservative. They are the last major desktop environment to default to X11 for example (though you will disagree with that view if you count XFCE as one of the major DEs).

[–] CafeFrog@lemmy.cafe 7 points 3 days ago* (last edited 3 days ago)

Cinnamon was written from scratch to reflect a more traditional desktop metaphor. It was not created from existing GNOME code.

Many parts of Cinnamon were forked from Gnome 3 and Gnome 2 (Mate).

XPlayer was forked from Gnome Videos (Totem)
Xviewer was forked from Eye of Gnome
Xreader was forked from Atril from MATE (itself a fork of Envince from Gnome 2)
Xed is a fork of Pluma (itself a fork of Gedit 2)
Cinnamon's compositor, Muffin, was forked from Gnome 3's Mutter compositor

Many other parts of Cinnamon are made from scratch, but it is not wrong the say it's also a Gnome 3 fork in many ways.