Attempting to use only the boxed in area. I’m not selecting them properly, I’m guessing as the ‘mask’ option is grayed out.
It’s hard to tell but I think I’m unable to select the ‘tool’ layer. I read the docs at Image Masking / Cropping but it doesn’t seem to work so simply. I changed the ‘box’ to something other than the tool layer to make is visible. I also tried making them on the same layer.
This is vector art and the ‘Apply Mask to Image’ is designed to work with bitmap raster artwork or images. You could use ‘Tools’–>‘Cut Shapes’ to isolate the section you want, deleting the remainder.