There is no official documentation.
Outlook Live:
https://outlook.live.com/calendar/deeplink/compose
Office 365:
https://outlook.office.com/calendar/deeplink/compose
Outlook Live:
https://outlook.live.com/calendar/deeplink/compose?path=/calendar/action/compose&rru=addevent&startdt=2023-08-09T19:30:00Z&enddt=2023-08-09T22:30:00Z&subject=Birthday&body=With%20clowns%20and%20stuff&location=North%20Pole
Office 365:
https://outlook.office.com/calendar/deeplink/compose?path=/calendar/action/compose&rru=addevent&startdt=2023-08-09T19:30:00Z&enddt=2023-08-09T22:30:00Z&subject=Birthday&body=With%20clowns%20and%20stuff&location=North%20Pole
required: yes
format: string
example: path=/calendar/action/compose
description: internal application path.
required: yes
format: string (addevent)
example: rru=addevent
description: action name.
required: yes
format: datetime (YYYY-MM-DDTHH:mm:SSZ) or date (YYYY-MM-DD, for all-day events) in UTC
example: startdt=2020-12-31T19:30:00Z
description: The start date for the event.
You can omit trailing Z, in this case script assumes that time specified in current user's timezone.
To specify all-day events use the YYYY-MM-DD format.
required: yes
format: datetime (YYYY-MM-DDTHH:mm:SSZ) or date (YYYY-MM-DD, for all-day events) in UTC
example: enddt=2020-12-31T22:30:00Z
description: The end time of the event, format as for startdt.
required: yes
format: string
example: subject=Birthday
description: event title.
required: no
format: boolean (true/false)
example: allday=true
description: whether event is all-day or not.
required: no
format: text
example: body=With clowns and stuff
description: description of your event
required: no
format: string
example: location=North Pole
description: set the location of the event.
required: no
format: boolean (any value means true)
description: toggle the "Skype meeting" button.
example: online=1
required: no
format: string
description: A comma-separated list of emails of required attendees.
example: to=santa@example.com,easter.bunny@example.com
format: string
description: A comma-separated list of emails of optional attendees.
example: cc=santa@example.com,easter.bunny@example.com
format: string
example: reqresponse=true
format: boolean ("true"/"false")
description: Allow forwarding.
example: allowfw=true
format: boolean ("true"/"false")
description: Hide attendee list.
example: hideattn=true
format: string (enum)
options:
freetentativebusyoofworkingelsewherenodata
format: any
Description: "Skype meeting" flag.
description: Unknown, probably Event id.