> I'm sorry, the default value of w32-pass-lwindow-to-system is t. I dont' change w32-pass-lwindow-to-system in init file.

So, let's recapitulate.

- You start Emacs 27.0.50

- In your init file(s), you do not change the default value of w32-pass-lwindow-to-system

- While Emacs has the focus, if you press an lwindow combination, Emacs catches it and it is not passed back to Windows.

- So, from inside 27.0.50, you cannot do LWin+R o LWin+D, etc.

- But this didn't happen with Emacs 26.2.

Am I right now?

If so, when you're inside Emacs 27.0.50, what does it say when you examine the value of w32-pass-lwindow-to-system? For example, with describe-variable.

Does still happen if you start Emacs with 

   emacs -Q

?