Transparency Panel - Mask Mode Overlay
When you enter the "Mask mode" in the Transparency Panel when adding a mask to an object. The background should switch colors or an outline around the artboard, similar to "isolated mode". To indicate that you're in that mode, right now you can click around thinking you're in that mode and not realize you have to switch back to normal mode by unclicking the mask.
-
I agree, the mode is not telegraphed that well, compared to Isolation mode... Ai displays 'Opacity Mask' (even as (<Opacity Mask>/Opacity Mask) ) in the document’s tab, but it’s not enough.
I suppose you know we can Opt/Alt the mask in the panel to toggle the current view between 'normal' and 'opacity' world, same as in Ps? It won’t mark it better, but at least it’d help to see what you are doing inside of it.