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I don't know where else to go, so I thought this might be a start.
My idea is, to copy a layer one could Control+LeftMouse click (onto the layer). I feel like that would be great, because it's quicker than dragging the layer onto the duplicate button.
(Disclaimer: I don't own Photoshop, I don't know if something similar is implemented.)
To duplicate a layer just press Ctrl+J (Cmd+J on Mac)