The preview build of Defender for Mac starts off focusing on signature-based malware detection. But over time, it’s expected to be able to detect and report the existence of malware based on what they’re doing to your system, much like the way it does on Windows.
It will also come with the Microsoft AutoUpdate service which ensures that the Microsoft Defender for Mac keeps itself up-to-date. The company has not announced where the Microsoft Defender will go next. That said, Linux seems to be a possibility, given the number of Tux (Linux penguin mascot) that appear in its promotional video. (Source: Microsoft via Ars Technica)