To list chat messages in application context, the request must be made from the tenant that the channel owner belongs to (represented by the tenantId property on the channel).
You will be getting the list of messages in meeting using the below graph api-
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GET /me/chats/{chat-id}/messages
We will check it internally if it any and get back to you.
Reference document-https://learn.microsoft.com/en-us/graph/api/chatmessage-get?view=graph-rest-1.0&tabs=http