Last I checked, they use Chromium Embedded for most of the UI, and native code to interact with platform-specific features such as the Touch Bar.

Any idea if Chromium Embedded has the same memory footprint as Electron? (That seems to be the main complaint about Electron that I've seen).

Electron is not anything much different than Chromium Embedded plus some native API hooks, so it's not the Electron parts that eat the resources, it's Chromium (and basically, it's the fact that the app is basically a web app that needs a whole layered and bloated rendering engine -DOM- and a slower runtime - js - compared to native).

Doesn't electron include the nodejs runtime as well?

Yes, which is just v8 + some system interfacing libs, not something that is slow/memory hungry by itself anymore than v8 alone is.

It would be slightly less since it is just Chromium versus Chromium + Node.js (as in Electron).

No idea. I personally have little tolerance for the amount of resources that Chrome uses, so I stay far away from its derivatives, which I have found to not be meaningful improvements.