I usually use a flow like this when triggering things with Teams and Power Automate:

1. Trigger: "When keywords are mentioned" - This is needed to get "Message ID"

2. Action: "Get message details" - Here you use the "Message ID"

3. Action: "Compose" or "Initialize Variable" according your needs

4. To get the message content use this expression in your compose or variable: "outputs('Get_message_details')?['body/body/plainTextContent']"