Google Search On Screen does not work I have the following problem: when I long-tap home button, a Google Now with search field appears, instead of Search on screen. I've tried to grant all perms to allow it use screen contents, but nothing changes.

I use Xiaomi Redmi 4x with AOSP Extended.
The feature you need is called Now on Tap.

According to Google blog, Now on Tap is available only in English, French, German, Spanish, Italian, Russian and Korean. All you have to do is set one of those as a secondary language in your phone settings to make it work.