Black and white as a layer

In the same way we can apply Match Look as a new layer, I'd very much appreciate if we could apply the Black and White function as a new layer too. Personally I currently use this way in Affinity Photo or Photoshop to desaturate my images by tuning the opacity of a B&W layer. But I'm presently obliged to edit the photos in Affinity Photo or Photoshop only to do so.