An integrated threat protection solution designed to detect, investigate, and respond to cyber threats across Microsoft 365 services.
The email is most likely a scam. Microsoft doesn't send unsolicited email to customers telling them that Microsoft Defender's coverage of one of their devices is turned off. If Microsoft Defender is turned off, Windows itself will notify you.
Do not do anything the email wants you to do. Do not sign in anywhere or call any number. Do not give the sender any information about yourself. Simply delete the email.