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