I don’t know why no one has mentioned this yet, but here is the one thing you need to know to survive as an “old” user of LingQ;
When you are in a lesson (in the new version), go to the gear wheel in the top right-hand corner of the screen. There you can turn OFF the automatic marking of words as “known”.
The system is supposed to remember this choice, but I have had it flip back so I always check it to make sure that the setting is the way I want it.
WARNING: You still have to watch out for the green “Complete Lesson” button on the last page of the lesson. Clicking on this will change all your blue words to “known” no matter what you have chosen in the settings. So don’t click that one until you have all the words marked as you want them.