There are a few troubleshooting steps that you can try to get your Arduino Nano back in Device Manager:
1. Try different USB ports: Sometimes, a USB port can malfunction and cause issues with your Arduino. Try plugging the device into a different USB port on your computer and see if it shows up in Device Manager.
2. Check the USB cable: Try using a different USB cable to connect the Arduino to your computer. Sometimes, the cable can be the culprit in these situations.
3. Restart your computer: Sometimes, a simple restart of your computer can fix issues with connecting devices to your computer.
4. Check for driver issues: It's possible that the driver for your Arduino Nano has become corrupted or outdated. You can try reinstalling the driver from the Arduino website.
5. Try a different computer: If none of the above steps work, try connecting the Arduino to a different computer to see if it's recognized there. If it is, then the issue is likely with your computer or its settings.
Hopefully, one of these steps will help you get your Arduino Nano back in Device Manager.