nvda screen curtain

Is there a nvda plugin that darkens the screen?
nvda is supposed to be 2019.3

Yes, it's included in 2019.3

You have to set the key command manualy in settings.

Where can it be downloaded?

It can't be downloaded, it's part of NVDA already.

Alfi, there's a setting called screen curtain, in your native language "képernyőfüggöny". If you tick that thing, your screen becomes dark. Although as others said, you can set a shortcut for it, so you don't need to go in settings and enable it manually.