No "None" Option For Lockcreen
Use this video as it seems exactly like your problem, try it then comment if it works https://www.youtube.com/embed/LV_7APlAvvc

So, basically what you need to do is :-


Go to settings and remove your pin/passwords if you have any.
Go to `settings>security' and at the bottom of the page you should see "clear credentials" tap on it and clear your credentials.


3 Now go back to lock screen settings settings and you should see the "None" option waiting there or you.