Blacks in Nitro manipulate the Black Point of the image, so it will shift values off of zero. It is a RAW only control.
Shadows and Highlights move those parts of the image with “some smarts” – however, I am looking into adjusting how those work to be more specific to those parts of the tonal range.
Each app has its own algorithms, and they are not published or documented, so each one will have its own feel.
I have made some videos about when to use Blacks (mostly when you have very dark data you want to recover and exposure or shadows doesn’t do what you want).