Deck and the touchscreen stopped working.
Thankfully, unless it is physically damaged—for example, if it has crashed—this is not a hardware problem but rather a software problem, which can be easily fixed.
All you need to do is first disconnect the Steam Deck from USB power. After you do that, you will have to somehow shut down the Steam Deck. There are many ways to do this. You can use the menu, controlling it with the D-pad. You may hold the power button for over 12 seconds. The fastest way I found is to hold the power and volume-up buttons simultaneously, which will shut down the Steam Deck very quickly.
After that, you need to release and press the power and volume-up buttons again and hold them until the Steam Deck enters UAV mode. Basically, this is the Steam Deck BIOS. Since the touchscreen obviously doesn’t work, you may try to control the cursor with the touchpads if they still function. If they don’t, you will have to use the D-pad and buttons to navigate the menus.
Here, you need to open the menu called “Power,” select it, and activate a mode called “Battery Storage.” When you activate this mode, the Steam Deck’s LED indicator will blink three times, indicating that it is now in battery storage mode.
Now, you have to take the original charger. Aftermarket chargers may still work, but I strongly advise you to use the original charger that came with the Steam Deck. Simply plug the charger into a socket and connect it to the Steam Deck. It should automatically power on. If it doesn’t, press the power button.
When the Steam Deck finishes booting, the touchscreen should be working just fine. As I mentioned earlier, this is thankfully not a hardware problem—it’s a software issue. At some point, Valve should release a BIOS update for Steam Decks that will fix this problem, so keep an eye out for BIOS updates for your device.