Currently we can get user's supported time zones using /me/outlook/supportedTimezones endpoint. This endpoint can return Windows Time Zones or Iana Time Zones.
The bad thing is that it returns alias and displayName only, no time zone offset or any additional information.
Because of that it's currently impossible to map Windows timezones response with Iana timezones response.
Why do we need that?
Example - display a dropdown with Windows time zones, but initialize selected item based on browser time zone (browser's Intl API gives you Iana name)