User Configuration > Administrative Templates > Microsoft Outlook 2016 > Outlook Options > Preferences > Calendar Options
User
HKCU\software\policies\microsoft\office\16.0\outlook\options\calendar
This policy setting allows you to prevent agenda view for Calendar search. If you enable this policy setting, Calendar search will default to list view. If you disable or do not configure this policy setting, it will default to agenda view. Note: This policy setting only applies to subscription versions of Office, such as Microsoft 365 Apps for enterprise.