Visual Studio and Android Device Monitor doesn't detect any devices

You most likely did not grant access to the device. Try to go into the developer settings on the smartphone and revoke the USB debugging authorisation. Then connect the phone to the pc and and wait for a popup on the phone which you should accept. After accepting you should see your device with adb devices.

You can also try to set the connection mode to MTP (instead of the camera PTP).

Hope it helps!