In the Microsoft Defender portal, connecting the Microsoft 365 app connector is part of enabling Microsoft Defender real-time protection integration for Microsoft Copilot Studio agents. The Microsoft Entra application configuration performed by the Power Platform administrator establishes the agent integration, while the connector enables the related protection output, alerts, and incidents to surface in Microsoft Defender.
Reference:
https://learn.microsoft.com/en-us/defender-cloud-apps/real-time-agent-protection-during-runtime
https://learn.microsoft.com/en-us/defender-xdr/security-for-ai/ai-agent-detection-protection