Try the security settings.Ok that seems to me a little weird, but, aren't there the options to set up PIN or pattern for the screen lock?
im only having Swipe and of course it not very convenient for us to have everyone unlocking our phone , haha.
I have installed Nova 7 launcher and i had a look there too in case it messes with lineage settings but i dont think i can find anything related to this there either.
It is a basic feature.
Regards,
Danny