User Configuration > Administrative Templates > Microsoft Outlook 2016 > Outlook Options > Preferences > Calendar Options
User
HKCU\software\policies\microsoft\office\16.0\outlook\options\calendar
By default, when a user accepts or tentatively accepts a meeting, Outlook creates a duplicate copy of the meeting with the new response status and a new entry ID. Outlook then deletes the old version of the meeting from the calendar. This setting allows you to roll back to the legacy behavior and prevent meeting regeneration.