Hi,
I have not Enabled that option on my Moto X4 and when you connect Phone over usb while unlocked you have option to select that connected device Controls What mode will USB connection be. Thus that was implemented to prevent Public USB chargers access phone and sensitive data.

Hello. First post. I had a really frustrating problem and cracked it.

[b]PROBLEM[/b]
Laptop running MediaMonkey (Windows 10). Sync to mobile phone by USB cable just would *not* work Moto g6 phone.

[b]SOLUTION[/b]
A hidden setting in the Moto g6 developer settings. On the phone, open 'settings', scroll down to 'about phone', scroll to the end of the list. Find 'build number'. Tap on 'build number' 7 (seven) times. This gives you 'developer' rights. Then search for 'default USB' configuration and set it to 'file transfer'. Fixed.

Somewhat unbelievable that . .
A. Any phone with a USB connection would default to 'charge only'
B. Changing the USB setting would be [b]so [/b]well hidden (when I read the instructions, I thought it was a joke and was almost expecting to be told to walk clockwise around a church at midnight).