XFCE is a lightweight desktop environment that uses GTK. It has its own GTK engine, window manager (XFWM), and its own set of apps built on top of GTK... most of them much are faster than their Gnome counterparts.

Thunar is much faster than Nautilus, XFWM is faster than Mutter, XFCE panels are much faster than the Gnome Shell, XFCE GTK engine is much faster than Adwaita... and the list just goes on and on. The result is a really fast and responsive user experience, that will run fast even in low spec machines.

I am not a fan of the default panel layout and overall configuration, but XFCE panels are easy to configure as well as highly configurable. You can create as many panels you want, position them anywhere you want and put any elements on them... There's even a way to create a macOS-like global menu, although I don't recommend it.