It's still React, and it's still too slow. The only difference is where the render is committed to (DOM vs Native UI)
Having a declarative rendering logic, a rendering runtime, the VDOM, diffing, re-rendering, update scheduling and everything else that React uses under the hood is always going to be slower than tailor-made imperative rendering.
And let's not even go down the rabbit hole which is concurrent mode and suspense, where React is going to be basically a black box more suited to quantum computing with the whole "render x times and settle on a result that it thinks is correct".
I'm not sure if it will take up more resources than the Xbox dashboard or office plugins, but I am willing to say "yes". The dashboard is quite simple compared to a full-fledged IDE which VScode is becoming, and I'm yet to see the whole Office suite, including the underlying logic, being ported to React Native.
Atom was ported to React at one point but they quickly abandoned it because of the bad performance. Microsoft followed suit and hasn't even bothered with React for VScode.
No commenting on the React thing, but yes I do think that VSCode has much higher performance requirements than Xbox dashboard or Office plugins.
VSCode has a very technical user base that will complain a lot if there is any kind of sluggish performance when doing live debugging. It's not just to work on small JS projects anymore. I use it to debug CUDA kernels on several processes at the same time and a lot of people have similar push-it-to-the-limit use cases.
If the user base was that technical, with performance requirements, they wouldn't be using an Electron based product to start with, when there are plenty of other native alternatives, including for CUDA debugging from Nvidia themselves.
Also do you consider that VSCode has higher performance requirements than XBox dashboard, or Office plugins?