The server will know what frame you were seeing when you pressed your button. So it rewinds it's state machine the appropriate number of frames (hopefully just 1), applies the input, and fast forwards again.

This may result in a visual glitch, but you won't have missed your target.

I wonder if you could use something like the RetroArch rollback solution[1] - render multiple versions of the stream, then pick the closest one based on player input. With a fast enough Internet connection, you could let the _client_ pick, then there is no lag.

Of course, the hardware you have to throw at it to do that quickly becomes ridiculous, unless you can come up with a way of efficiently rendering the multiple versions.

[1] https://www.libretro.com/index.php/retroarch-1-7-2%E2%80%8A-...

can't speak for Steam Link because I have one, but it was more headache than it was worth to get running.

That said, I had my Bootcamped MBP with a XB1 controller connected over Bluetooth and any input lag was negligible with the Assassin's Creed Odyssey Project Stream demo.