How can I save the following mask as a PNG image ?
I pressed Alt + Right-click on the mask to get the following image but I don't know how to export it
I think it's as simple as selecting all (Cntrl-A Win | Cmd-A Mac), copying that contents (Cntrl-C Win | Cmd-C Mac) and exiting mask preview, adding a new layer and pasting the copied contents into that new layer (Cntrl-V Win | Cmd-V Mac) - you then can export it as a .png as you would any other contents of a typical layer.
The way it works to me:
Select the layer mask.
Press Ctrl + A .
Then press Ctrl + C .
Create a new Layer and press Ctrl + V .
Now you can export it to png, jpg, etc.