Moving Map functionality is provided by Simlink on your FS machine sending your FS coordinates to our servers. When you run Charts on your tablet the charts are downloaded to your tablet via the internet with our servers adding the magenta aircraft icon. There is no local connection between FS and Charts.
I haven’t tried USB tethering, so cant comment if the tethering provides a transparent internet connection for the tablet. I read there may be some slow down in internet connection via tethering, which could be an issue.
I’ve used an app before that tethers the tablet to the windows PC and makes it act as another windows monitor. There are more options than the one app I’m sure. Have to run piece of software on PC and Tablet and the tether connection. You can then drag any app, such as navigraph to the tablet window. Good luck!