There is no way to get a notification when a file/folder is added within a channel in a team.
You can get the notification for Get all files folder in channel using below resource path.
Changes to channels in all teams:
/teams/getAllChannels
Changes to channel in a specific team:
/teams/{id}/channels
You can refer below document for getting the notification for Teams channel resource.
https://learn.microsoft.com/en-us/graph/teams-change-notification-in-microsoft-teams-overview
https://learn.microsoft.com/en-us/graph/api/resources/channel?view=graph-rest-1.0#methods
Thanks,
Nivedipa
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