I wrote a little essay a few ago about pirating games on SteamDeck, I am not sur it is allowed here. I didn't saw any rules against.
If it is feel free to pm me I will remove my post.
Hope this help other with low budget.

No need get window. You need somes tools though.

From the stock app market (called discover) :

• Transmission
• Lutris
• ProtonUp-QT to install ProtonGE

From GitHub:

• Decky (and the addon SteamGridDB)

On desktop mode.

I download my games as torrent from dodirepack or fitgirl with the software transmission(from stock appshop).

Once I have a game I use Lutris(from stock appshop) to execute the installer.
Install games on :Z Wich is the steals file system.

Then I add the game to steam on desktop mode.

I set the compatibility in the game options mode on proton or protonGE.

And I rename the game to their steamid to be able to search for contrôler config. (Find steam game I'd on the site SteamDB)

In game mode

I then setup images for the games with the addon SteamGridDB installed from Decky (and addon loader for steamdeck)

If I have trouble running game I use protonGE which I installed with ProtonUp-QT (from stock appshop)