Hi @karimabdelrazek ,
Could you please share more details about your scenario? What kind of calendar would you like to retrieve, SharePoint group site calendar list or O365 Outlook calendar?
If you want to retrieve calendar apps from SharePoint group sites, which are just like lists, you could create connectors to connect with them:
1. Choose Sharepoint connector

2. Choose a site

3. Type in the calender list name then check, click connect:

You could find the calendar name in Site contents.
After connecting to all calendars of group sites, on the calendar contents screen, add a Drop down with the Items of a collection for users to select.
[“Group1 Calendar”, “Group2 Calendar”, “Group3 Calendar”]
Then you could use a Gallery with the Items:
Switch(Dropdown.Selected.Value, “Group1 Calendar”, ‘Group1 Calendar’ , “Group2 Calendar”, ‘Group2 Calendar’ , “Group3 Calendar”, ‘Group3 Calendar’)
Note:
App users should be an owner or member in those groups and with the permission to edit so that it would be able to update or modify the calendars.
If you want to retrieve all calendars of O365 teams from O365 outlook, I’m afraid there is no way to achieve your goal. Users could only get the teams list owned by themselves, you are not able to retrieve all teams into a dropdown for users to select. And user could only see calendar events owned by itself.
Hope it helps.
Best regards,
Community Support Team _ Jeffer Ni
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