I want to opacify the whole window when I open a popover
You could use an object with transparency a hide condition to achieve this (see attached file), but you may want to look into using a Card Window instead, since a card window has this as a built-in feature.
Here is a method I have used which has a nice effect for some applications. I don't recall how I found the post, but found it in my bookmark archives. I'm not sure if I originally found it just searching the Web or if was suggested here in the forum.
Edit to add there's a sample file available on the blog post linked.
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