To start, I have just purchased the LG Stylo 3 plus and ran right into this situation. TO repeat the basics you need
With Android Studio shut down...
- Turn on Developer options (tap 7 times on build number in settings
- (Settings>System>About Phone>Build Number
- Turn on USB Debugging in Developer Options
- (optionally) check on the type of USB connection, MTP or PTP should
- (Optionally) Because I did it, also do a revoke USB tap.
Here was the key for me. I needed to install the LG USB Windows Drivers for my Windows 7 (I'll try 10 tonight and update). Go to this page
LG Drivers and firmware
and either type in model number or browse to find device. LG has a nice interface to install the Windows Drivers. I recommend the Support tool to verify the device as the up to date drivers as well. Start Android Studio and to test I just started the app in debug mode and went through the process of setting up ADB for using the new;y connected device.