Xbox Remote Play on Steam Deck from a friends house possible?

Yes, it is possible to use Xbox Remote Play with your Xbox on your home WiFi network and Steam Deck on your friend's WiFi network, as long as both networks have a stable and reliable internet connection. Here are the general steps you can follow to set this up:

Set up Xbox Remote Play on your Xbox: Ensure that you have the latest version of the Xbox app on your Windows 10 PC and that your Xbox is updated with the latest software. Then, follow the steps to set up Xbox Remote Play on your Xbox by opening the Xbox app, clicking on the "Connection" tab, and selecting "Set up a new Xbox."

Connect your Xbox and Steam Deck to the respective WiFi networks: Ensure that both the Xbox and Steam Deck are connected to their respective WiFi networks. You may need to enter the network password if it is a new network.

Ensure that both networks have a stable and reliable internet connection: Make sure that both networks have a stable and reliable internet connection to ensure smooth gameplay.

Connect to your Xbox on the Steam Deck: Open the Xbox app on your Steam Deck and click on the "Connection" tab. Click on "Add a device" and follow the prompts to connect to your Xbox.

Once you have successfully connected your Steam Deck to your Xbox, you should be able to stream games from your Xbox to your Steam Deck over the internet

You would have to install windows on Steam deck

That’s not possible except for Cloud Streaming. Steam Deck runs Linux, and the Xbox app doesn’t support PC streaming.

You’ll have to install Windows to play Windows Store games on Steam deck natively or stream using a third party solution from a Windows PC

Xbox remote play is primarily designed for Xbox consoles to stream games to other devices like PCs, phones, and tablets. The Steam Deck, being a handheld gaming device running on a modified version of Linux with SteamOS, might not directly support Xbox remote play.

The save file from Gamepass would not cross over to Steam. The work around to play on Steam deck would be to do so by accessing Gamepass on the Steam deck.