Hello James Naadjie,
Thanks for reaching out.
Based on the description, it seems like you are looking for an equivalent delegated permission in MS graph API that can be used for the Chat.Read.All application permission. The Chat.Read.All application permission is only available as an application permission, which requires an application to be configured with admin consent.
Delegated permissions are used to access resources that the signed-in user has consented to. There are some delegated permissions that can be used with a Teams tab application, such as Chat.Read, Chat.ReadBasic, Chat.ReadWrite. These permissions allow the application to read and write messages in the signed-in user's chat conversations and channels.
However, in your use-case, API requires role permissions on the request that would either be fulfilled by an application permission or a resource specific permission.
Refer below links for better understanding:
Intro to Permissions and Consent: https://learn.microsoft.com/en-us/azure/active-directory/develop/permissions-consent-overview
Resource Specific Consent:
Hope this helps.
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