Is it possible to reach 0nits on the display, because it is very bright even in minimum level and it is not so eyes friendly during the night for example? How to do that? On that link is written that option is available. https://www.blackview.hk/blackview-371/

I use the app Dimly for that purpose. There is no option in the system itself to reduce the screen brightness other than the slider, which - I agree - leaves the screen too bright at night.