Steam has this nifty little feature called 'Steam Stream'. It is different to Steam Link. Steam Link is where I can play STEAM games on something like my Apple Vision Pro. Steam Stream is a where I play STEAM games on a device which already has STEAM installed onto it. It's how you can play Windows-Only games on Mac, for instance.
The first thing to do is configure your WiFi. Both the STEAM DECK, and your Windows PC must be connected to the same WiFi Network. When I tried Steam Streaming on different Networks, it didn't work. Maybe that's just a me thing, though. I encourage you to do your own testing.
If your PC is connected to, lets say, 'ΙΗΣΟΥΣ Ο ΛΟΓΟΣ', then my STEAM DECK would also need to be connected to that same Network.
If everything goes well, your STEAM DECK menu screen, whenever you select a game, should like this.

Notice the arrow pointing down. You'll want to select that, and choose your Desktop name. I will refrain post a screenshot of that, as I do not wish to give out sensitive information.
Your menu should look like this after you're done. Notice the 'Stream' icon.

Select that option, and you're 3/4 done. You might have to authenticate the stream. Steam will sometimes give you four numbers you must type into the computer you're streaming from for safety reasons.
It should look something like this; sorry for the bad quality, I had to get the photo to under 2 MBs.

The game will play on BOTH your Desktop, and STEAM DECK. However, it'll be controlled from the STEAM DECK, sort of like the WiiU.
Except not nearly as cool.

The first thing you'll notice about Steam Streaming is this. The Audio.
Steam Streaming plays the audio through whatever device you're streaming to. If this isn't a problem for you, and you enjoy the STEAM DECK's speaks just fine, then you won't have to do this next step.
If you want your normal Audio set up, headphones or whatever, then you'll need to connect that set up to your STEAM DECK, and not your main computer. Here's an example.
Let's say I use a Bluetooth speaker as a mini-soundbar; I typically use a speaker setup because of my Tinnitus. I want to use it for Steam Streaming.
First thing I have to go to, is my PCs Bluetooth options. I scroll around until my find my Speaker; in this case, a Sony SRS

I hit the three dots on the right, and select the option 'Disconnect'.
I then go onto my STEAM DECK, and to the Bluetooth Settings.

Next thing to do is pair the Speaker, or whatever you're gonna use, to your STEAM DECK. Each device is different, but it should look something like this after you're done.

Whenever I adjust the volume, either on my STEAM DECK, or my Speaker, it'll look like this. Take not that the Speakers name is in the Volume adjustment. If yours doesn't show it, it didn't work.

The only thing that will improve bad Latency and Input Lag is a better WiFI connection. You can lower the resolution of both systems to shore-up bandwidth, but that'll only take you so far. Not much I can do to help. Sorry :(

We could not live with our own failures. And where did that bring us? Back to the WiiU.
I hope Valve and other Devs do something with this. The WiiU was so ahead of its time, and some really cool game-play can come from having your controller be a screen too.