MIT is the standard OSS license for Microsoft stuff that is open source. You also see Apache for some projects that predate standardization on MIT, and GPL where there's no way to avoid it (i.e. when you have to build on code that is itself GPL).

That said, peak OSS at Microsoft is already past. These days, it's all about advertising products as OSS while quietly close-sourcing parts of it (e.g. just about the only thing in VSCode that's fully open source is JS support, every other language extension is closed to some extent).