User Configuration > Administrative Templates > Microsoft Outlook 2016 > Miscellaneous
User
HKCU\software\policies\microsoft\office\16.0\outlook\addins
This policy setting allows you to disable installation of web add-in equivalents of COM add-ins on the switch to new Outlook. The add-ins available for migration are listed in https://aka.ms/newoutlooksettings. Learn more about Outlook web add-ins at https://learn.microsoft.com/office/dev/add-ins/outlook/outlook-add-ins-overview. COM add-ins do not work in new Outlook for Windows. By default, users in the organization will get the option to install available web add-ins, in place of COM add-ins, when they move from classic Outlook for Windows. If you enable this policy setting, users will not get the option to install web add-ins in place of their COM add-ins. If you disable or do not configure this policy setting, users will get an option to install web add-ins in place of their COM add-ins.