This Error Code 21, Windows is removing this device shows up when Windows is in process of removing a device, but the process is not yet complete, This error code is usually temporary, and goes away with time, but if you managed to get your sharp eyes on this, then simply restart your Windows 10 PC a couple times to remove this.

That said if it still doesn’t resolve it for you can:

1] Try performing a clean boot of Windows 10 PC, and then reboot back using normal mode.

2] Run Hardware and Devices Troubleshooter and it should help you get rid of those messages.

This error is something you should be least bothered about.