Godot has many parts besides the UI and graphics stack, and most of its dependencies vendored and statically linked. See the thirdparty folder for a list: https://github.com/godotengine/godot/tree/master/thirdparty
The official binaries include everything, but many of the larger bits are optional and can be disabled during build time to reduce the size of the executable: https://docs.godotengine.org/en/stable/development/compiling...
The fact that the Godot editor includes the Godot runtime along with its own UI- and graphics stack (if I'm not mistaken?) in such a small bundle makes this even more impressive to me.