Eraser / brush to edit the automatially generated mask.
use apple pencil on ipad to edit masks!!
Masking is strangely limited without the ability to brush edit the mask. I find myself going back into Snapseed, which does this well.
Really need this for portrait fotos. The ai masks are a GREAT help but for example eyes cannot be selected or excluded (which is an area you definitely want to treat differently than eg skin)