How to add a new selection to the old one in a layer mask?

Question

Adobe Photoshop

For example, I selected the first part of the object with the pen, made a selection, inverted and made a layer mask. Those. now part of this object is selected on the layer mask. I want to select the second part and also add a mask to the same layer so that both of these parts, which I have selected, pass as a single whole on this layer mask. Thus, you need to add a new selection to the old one on the layer mask and make them merge. With what can this be done?

Answer 1

If I understand correctly, then select the second part, with Alt pressed, click on the mask icon itself (thereby you switch to its display as a layer) and apply the fill to the selection (or any other operations, be it a brush, etc.).