Version: 2021.3
Set a layerMask
Remove a layer from a layerMask

Add a layer to a layerMask

To add a layer to a layermask, use the logical OR operator on the original layermask and the layer to add.

originalLayerMask |= (1 << layerToAdd);

Additional resources

Set a layerMask
Remove a layer from a layerMask