The SteelSeries Stratus Duo is designed to provide haptic feedback (vibration) during gameplay on compatible devices. If your controller isn't vibrating, it could be due to a hardware or software issue. Maybe try some of this
# Check the software: Make sure you have the latest firmware installed on your controller and that the device you're using it with is compatible.
# Check the settings: Check the settings on the device you're using the controller with to ensure that vibration is enabled.
# Try a different device: If the controller isn't vibrating on one device, try using it with another device to see if the issue is specific to that device.
Good Luck!