I want to create a "gaming streaming platform" like Stadia as a weekend project, does anyone know where to get started? Basically where the input device and the game are in different machines.

For off the shelf shadow.tech has worked pretty reliably for me, even to the point of being usable for streaming vr using alvr (uk based).

For diy you can use moonlight / sunshine or steam remote play. I find latencies lower than around 30ms perfectly playable for everything except twitch shooters etc.

For true diy look into leveraging nvenc or equivalent hw encoder using a “zero latency” profile and build on top of UDP. TCP could be feasible for client input -> remote traffic, but even then building a minimal custom reliable layer on top of UDP probably makes sense to avoid nagle type issues. If you want to support arbitrary input devices (joysticks, wheels etc) that can’t be represented as an Xbox controller things will get pretty tricky. Especially if those devices require drivers, at that point your into proxying usb.

DIY in a weekend? Definitely.

True DIY in a weekend… probably not :)

Sunshine is a great open source game streaming stack, and has client applications for tons of platforms, usually under the name "moonlight". Bazzite makes setting that up on a host (machine running the game) dead simple.

Moonlight does this if you are just looking for a solution.