This is a program to emulate a game controller on the Steam Deck when connected over USB to another computer.

The USB port on the Steam Deck is a USB Dual Role Port. This means that, like most phones, it can act as a USB host or device. This is possible with the DWC3 (DesignWare Core SuperSpeed 3.0) controller in the AMD CPU.
Using LibComposite, we can emulate a wide variety of USB devices. In this case, an HID device is emulated that has some game controller inputs.

• A password set for the deck user
• SSH enabled

On the Steam Deck, boot into the BIOS by holding the VOLUME UP button and pressing the power button and go to setup utility. Navigate to Advanced>USB Configuration>USB Dual Role Device and change from XHCI to DRD. Then Exit>Exit Saving Changes.

In a terminal, run

curl -s https://raw.githubusercontent.com/Frederic98/GadgetDeck/main/setup | sudo bash

This should download and install GadgetDeck and everything it needs to work. When this is done, you should have a new item in your Steam library under non-steam.
❗It is possible that it shows up as a blank tile without a name. This should be fixed after a reboot.

Start GadgetDeck, and assign actions to all inputs appropriately. When this is done, connect your Deck to a PC and test if the keyboard and mouse work.

On your computer, search game controllers and open Set up USB game controllers. Move the Steam Deck joysticks, and this should be reflected on your computer.

In Steam on your computer, go to settings->Controller->General controller settings and enable Generic gamepad configuration support.
Then, click the steam deck and map all the buttons to a controller layout.

Not really necessary. But, to stop the USB gadgets, either reboot the Deck, or, in a terminal, type systemctl stop gadget-deck-base.

• Ethernet gadget for local multiplayer by connecting two Steam Decks to each other (Might need to disable charging on both to prevent one from draining the other)
• MTP gadget to browse Steam Deck files from computer
• UVC gadget for streaming game to computer without the use of an HDMI capture card