02-14-2023, 08:49 PM
Quote: ...I'm not sure what I did wrong...
Add your layer mask (white) to the layer. No need to add an alpha channel, the layer mask does that.
If you have a green border, you turned Layer -> Mask -> Show Layer Mask ON Turn it OFF
You make the layer mask active by clicking on its icon in the layers dock. Active it has a white border. Then you paint on the canvas Black to uncover / White to cover/ grey(s) for semi-transparency.
A quick demo animation of that: https://i.imgur.com/1p4fjPr.mp4