moto x4运行Android 8.1.0。尝试将手机连接到任何Windows 10 PC失败。手机开始充电但在设置下，USB表示未连接。手机不会出现在PC上的设备管理器中。一个Moto E4运行Android 7.x没有问题，允许我在每个内部和SD上看到文件。
Moto X4 running Android 8.1.0. Attempts to connect the phone to any of my Windows 10 PC fail. The phone begins to charge but under Settings, USB says Not Connected. The phone does not appear in Device Manager on the PC. A Moto E4 running Android 7.x works without issue, allowing me to see files on each internal and SD.
There are reports that the update to 8.1 has disabled USB storage functionality but there is a fix on the way (time table unknown). The only work around right now is to disable your lock screen, reboot, then you can connect it. This worked for me but it will stop working again as soon as you re-enable your lock screen (which obviously everyone should).
Sorry, but long story short, the update broke it and you'll have to wait for a fix.
A Motorola agent confirmed the issue on the official Lenovo forum