User Configuration > Administrative Templates > Microsoft Word 2016 > Word Options > Save
User
HKCU\software\policies\microsoft\office\16.0\word\options
This policy setting allows you to configure the file format compatibility dialog box when saving a file as an OpenDocument text file in Word. If you enable this policy setting, the file format compatibility dialog is not displayed whenever you save as an OpenDocument text file in Word. If you disable or do not configure this policy setting, the file format compatibility dialog is displayed when you save as an OpenDocument text file in Word.