Here is the bottom UI. In it there is a button or two. One opens the and another, does

Here is the dialog. This takes over the whole screen. You can close it with this But alongside this, lives another dialog, that, when active, needs to be above this dialog. We can show this other dialog by pressing this
I am the top most popover, I live in the top layer, but things below can be interacted with. Sadly, I cannot be interacted with, click this button and weep.