If you want to duplicate a layer mask in Photoshop, there are a few different ways to go about it. The easiest way is to use the Copy Layer Mask command (Ctrl+J/Cmd+J on a Mac). This will copy the mask over top of the original layer, and you can then edit the copy as needed. If you want to duplicate a layer mask without copying it, you can use the Layer Mask Mode menu option (LMB) to change the mask’s mode to “Copy.” Then, using the Selection tool (V), drag the bottom edge of the mask up so that it covers all of the content on the original layer. When you release your mouse button, Photoshop will create a new copy of the layer mask based on this selection. ..
