Sorry @c.pfaffenbichler
You lost me there!
For the below instructions, would you have a guide or video that you can point me to please?
"If you need to use it in many files you could create a Solid Color Layer (though you may want to make the hidden side of the mask proper black) with the inverted Mask and use it as a linked Smart Object or put in in the Library tu use as a Knockout. "
By putting multiple Layers in a Group with the Blend Mode »Normal« one can use a Knockout-Layer with Fill 0% one those.
By using a Linked Smart Object one can use the same Knockout in multiple files and, if onechanges the SO itself, update it the next time one opens the layered images.
A Library Smart Object may be more convenient for placing, though.



