Windows 10 Boot Camp shuts down and boots into macOS overnight

Solution 1:

Windows is probably rebooting on its own, and macOS is currently set as your default operating system on boot.

You can make Windows the default in macOS by opening System Preferences > Startup Disk and clicking on Bootcamp. Mine has macOS as the default boot:

Or on Windows, by opening the Bootcamp preferences, clicking the Bootcamp drive then clicking [Ok] or [Apply]:

If you want Windows to stop automatically rebooting it's a bit harder to do, because that's a Microsoft thing, they apparently like to reboot regardless of what you're doing even after telling them you are working and can't update now.

Here are instructions to disable automatic updates on Windows. You will then be able to update manually when you want, but after I think 30~60 days or so without updating, your Windows will force you to update. Alternative link to disable automatic updates.