https://learn.microsoft.com/en-us/powershell/module/exchange/set-organizationconfig?view=exchange-ps#-postponeroamingsignaturesuntillaterhttps://learn.microsoft.com/en-us/powershell/module/exchange/set-organizationconfig?view=exchange-ps#-postponeroamingsignaturesuntillater has changed to this:
We recommend that independent software vendors (ISVs) onboard to the https://learn.microsoft.com/en-us/javascript/api/outlook/office.body#outlook-office-body-setsignatureasync-member(1)based on https://learn.microsoft.com/en-us/office/dev/add-ins/outlook/autolaunch.
We have no plans to support roaming signature management in the Microsoft Graph API.
So it looks like this is not going to happen. We at IdentityStream have consequently developed an Outlook add-in using the signature API and event-based hooks to fetch and insert the proper signature per user from a centrally managed signature store. We are rolling out to the first customers this month.