Hi there. If you go to smart unlock in the settings, thee you can setup the face recognition. It does unlock the screen if recognise your face, but still you have to manually swipe up the lockscreen, just not asking for password. When it recognise your face the little lock symbol in the bottom middle "opens up" and then you can swipe up the screen without password. I hope it helped, do not expect same like Face ID, but still useful.
Hey. I got a method to get the option.
Install this framework by google.
Its verified. Don't worry about viruses or anything.
I think the stock 8.1.0 doesn't have this framework installed built-in.
After installation check the Smart Lock option. You should see the Trusted face option.
It works on my Nokia 6.1