@Romeo Alcantara - It seems that Copilot Studio-created agents are not directly available through the "Add People" option in user chats. Instead, these agents can be shared via a link after they are created.
This link allows specific users or groups within your organization to interact with the agent in their chats.
Ref Docs:
1.https://learn.microsoft.com/en-us/microsoft-365-copilot/extensibility/copilot-studio-agent-builder-publish
Thanks,
Nivedipa