Unknown sources permissions don't work

[rizla2]

I'm trying to install an app from unknown sources on my Xiaomi a2 with android one. I've allowed Chrome to install, doesn't work. Tried the same with files, file manager, download manager etc. All finishes with app not installed. How to make it happen? I do not have any "admin" apps people mentioned on other post, and I did manage to install one app yesterday and that is it, all the apps after that just won't install. ?