Policy
Show the File Format dialog
This policy setting allows you to control whether the file format dialog has already been shown to the user. If you enable this policy setting, the dialog won't be shown again. If you disable this policy setting, the dialog prompts the user to select a default file format on each boot until one is selected. If you don't configure this policy setting, the dialog prompts the user to select a default file format on each boot until one is selected.
c8dcd40fd62f L_ShownFileFmtPrompt Registry
Copy registry mappings
HKCU\software\policies\microsoft\office\16.0\registration\shownfilefmtpromptpolicy (enabled) = 1
HKCU\software\policies\microsoft\office\16.0\registration\shownfilefmtpromptpolicy (disabled) = 0 Policy notes
This policy setting allows you to control whether the file format dialog has already been shown to the user. If you enable this policy setting, the dialog won't be shown again. If you disable this policy setting, the dialog prompts the user to select a default file format on each boot until one is selected. If you don't configure this policy setting, the dialog prompts the user to select a default file format on each boot until one is selected.