I want to create a simple mask

I want to create a mask, just like you always used to be able to do under opacity in effects controls. However that option has vanished. There’s the stupid object mask tool and I can hold select it to get the  “rectangle mask tool.” This lets me select an area, presumably to mask it. A red overlay appears, this overlay’s color can be changed and I can select the “none” option. HOWEVER what the MASK DOES NOT DO is make the contents in or outside of the mask disappear. You know, the one and sole function of a mask. Maybe I am blind and don’t see it but I want my selection to ACTUALLY DISAPPEAR like a mask is SUPPOSED TO DO. How do you do this and why did premiere make such a stupid update turning something that used to be painfully simple into a three ring circus performance?