If you develop an office.js application, which in turn cannot be released in AppSource (due either in-house or on-premise installation), it is not possible to set the default Meeting Provider for Outlook.
As stated in documentation:
https://learn.microsoft.com/en-us/powershell/module/exchangepowershell/set-mailboxcalendarconfiguration?view=exchange-ps
This is because:
-DefaultOnlineMeetingProviderOnly supports a static (?) enum list:
AlibabaDingTalk
AmazonChimePrivate
AmazonChimePublic
AppleFacetime
BlueJeans
ClaroVideoconferencia
FacebookWorkplace
GoogleMeet
GoToMeeting
JioMeet
RingCentral
SkypeForBusiness
SkypeForConsumer
TeamsForBusiness (This value is the default.)
Webex
Zoom
What I propose, is to introduce a new enumerable to that list "Custom", in combination with a new argument e.g. -DefaultCustomOnlineMeetingProviderId.
The value here could either by the manifest ID (GUID) or ProviderName?
Then the combination ... -DefaultOnlineMeetingProvider Custom -DefaultCustomOnlineMeetingProviderId <Example>
Would allow organizations, who can not for whatever reason get into that static list, allow a flawless experience in Microsoft Outlook.