You have a Microsoft 365 E5 subscription.
Automated investigation and response (AIR) is enabled in Microsoft Defender for Office 365 and devices use full automation in Microsoft Defender for Endpoint.
You have an incident involving a user that received malware-infected email messages on a managed device.
Which action requires manual remediation of the incident?
Isolating the device requires manual remediation. In Microsoft Defender for Endpoint, actions such as isolating a device are considered manual response actions that need to be initiated by an administrator. Automated responses generally cover tasks like quarantining malware or blocking a file, but isolating a device to contain a threat typically requires human intervention to reduce the impact on organizational operations and ensure an effective containment of the infection.
https://learn.microsoft.com/en-us/defender-endpoint/respond-machine-alerts Important Defender for Endpoint Plan 1 includes only the following manual response actions: Run antivirus scan Isolate device Stop and quarantine a file Add an indicator to block or allow a file. Microsoft Defender for Business does not include the "Stop and quarantine a file" action at this time.
hard deleting the email message
https://learn.microsoft.com/en-us/defender-endpoint/respond-machine-alerts
https://learn.microsoft.com/en-us/defender-xdr/m365d-remediation-actions
This link is for XDR, not MDE. And if this were an accurate citing then the question would be rather terrible because the only thing not listed in that source is containing a device