If the Copilot Studio agent flow uses any connections such as Office 365 or any other connector, we can specify which credentials the flow can use — a Service Account or end user credentials. In case of end user credentials, the agent will pass the credentials to the flow.
Go to agent → go to flows → open flow → connections and manage connections.
If you click on this you will see the options of adding connections along with 'Provided by run only user'.
This gives you full control over whose credentials are used when the agent triggers a flow — whether that's a shared service account or the individual user interacting with the agent.