I tried to add a overlay window onto app in full screen mode but failed

As the topic mentioned, I want to add a overlay window onto Apps that are in full screen mode, trying to create some blur effect on the screen. But Apple seems to treat full screen mode Apps differently as a "space."

So currently I can only apply the blur effect like this. (This is my Desktop page) But When it doesn't affect the full screen mode Apps. (For example: My Xcode)

And I know some of the App down this kind of stuff. Like this

This is my current code. Hope someone can tell me how to solve it.

[https://codefile.io/f/QTV04ecKup?] This is the link of the code.

I tried to add a overlay window onto app in full screen mode but failed
 
 
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