Seems so. Checked the sources and there's no upload/download. And testing it I can confirm the network tab in the dev tools is silent. Everything work local side. Probably with some additional work this could be converted to a PWA (Progressive Web App) and work completely offline.
For a game it has to be Outer Wilds...
And please do yourself a favor and play it the one time you're allowed in this lifetime if you've not yet done it, as you can.
I'm currently playing the Amazon version.
As it's a code for gog, you can easily use heroic launcher, it works wonderfull.
Go to desktop mode, in the discover app install heroic launcher.
Then open it, go to the store and login to gog. Now you can install any gog games and add it to steam directly from heroic launcher. Then it works perfectly out of the box in game mode.
I had a "portable" 286 PC with DOS. And two games. Bubbles Bubbles and a game with two chimps throwing Bananas at each other.
This may work if the developer is a possible client too like in this case. But I feel that's the exception.
Do what the clients want and not what developers, designers or management want.
Prepping as already suggested helps a lot. But make use of appliances too.
A fish fillet can cook in the oven in 40 minutes but does not require care while cooking.
A slow cooker is a god send. You can start your ribs the night before and they'll be ready for lunch.
Then pasta takes 10 minute to cook and you can just prep some veggies/souces in advance.
I would add Outer Wilds to the list.
You can really only play it once in a lifetime but I think it's the best video game experiences available.
Honorable mention for Tunic and Cocoon for the same reason