Microsoft revisits the Priority Account Protection in 365:  (Microsoft 365 Defender): Applying a higher level of protection to accounts likely to be targeted by attackers is a more compelling offer as the last thing you want is for an executive to fall foul of a business email compromise attack or other phishing attempts like the recent Office VoIP voicemail notification. The aim is to deliver early warning when priority accounts are being targeted by malware and other threats. This feature requires Microsoft 365 Defender and is enabled when people have Office 365 E5 or Microsoft 365 E5. To learn more, view this Ignite video.

Few reference articles for this and a few other new features: 

Looking at Microsoft 365 Priority Accounts Again
Microsoft Defender for Office 365 to Get Advanced Threat Protection for Priority Accounts