Windows 10 Boot Camp shuts down and boots into macOS overnight Only when I wake up in the morning I find my MacBook Pro 16” in Catalina. At night the computer is in Windows 10. This happens only overnight. Throughout the day my computer remains in windows 10. Even whilst asleep. Is there something causing the computer to shut down?
Is Windows set as the default boot source in macOS's System Prefs > Startup Disk? 

If not, then Windows could be initiating the reboot for its own housekeeping purposes [which it tends to do a lot], but macOS is taking precedence at the actual reboot.