DualSense not working on Steam
First, check the controller itself works: open the tester and press a button. If the tester sees it, the controller and connection are fine, and the problem is in Steam's settings.
1. Turn on PlayStation controller support
In Steam, open Settings → Controller and make sure Steam Input is enabled for PlayStation controllers. Restart Steam after changing it.
2. Check the game's own Steam Input setting
Right-click the game in your Library, choose Properties → Controller, and try the other options. Some games work best with Steam Input on; games with built-in DualSense support may work better with it off.
3. Make sure Steam sees the controller
Steam's controller settings list connected controllers. If the DualSense isn't listed, reconnect it. A USB-C data cable is the most reliable test. If it's listed but buttons are wrong, use Steam's controller test or calibration options there.
4. Close other controller apps
Running Steam Input together with another DualSense or DS4 tool can make the controller show up twice or not at all. Close the other tool, or turn Steam Input off for that game, so only one is in charge.
5. Use USB for PS5 features
Haptic feedback and adaptive triggers in PC games usually only work over a USB cable, and only in games that support them. Over Bluetooth the controller still works as a normal gamepad.
6. Reset and update
Reset the controller with the small hole on the back near L2 (hold a paperclip in it for about 5 seconds), then reconnect. If you have a PS5, update the controller's software there. See the PS5 guide for the menu.