Is there a way to keep a word as unknown/not known without creating a LingQ?
What I think you want is for some lingqs not to show up in your flash cards. You still should turn them into lingqs. Just tag those words you want to know as you lingqed them. Include a tag such as "learn" or even "learn-2020". Then, when you want to review your flash-cards choose that tag.
It's the best way for many reasons. First, in Lingq you're supposed to turn any word you don't know into a lingq, that's the way the system works. Second, you'll probably want to learn some of the words you're dismissing now at some future point. Third, you'll feel overwhelmed by the number of words you want to learn no matter how carefully you choose them now, you want a flexible system that allows you to further filter them out in the future. With tagging you can always go back and change the categories or introduce new ones.
I think the best thing to do would be to set up a separate system for words you want to focus on learning. A separate Anki deck or Flashcards Deluxe. As you see, the flash cards in Lingq are really only useful in the lesson they’re connected with. From what I understand, Steve doesn’t really focus on flashcards outside the lesson they’re in. He may review them at the end of the lesson, but that’s about it.
When I come across a LingQ for a second or third time and I still don’t know what it is, then that may indicate it’s an important word I want to focus on, so I’ll add it in a phrase on a flashcard in one of my decks. Once I’ve learned it, then I can mark it the next time I come across it.
As you have said, you can disable "Paging moves to known" to prevent words switch to blue to white automatically when you page. However even in that case, when you complete a lesson, all blue words will became known.
There is no reason to keep blue words. The idea is that you either need to learn them or they are known. (or you can ignore words).
Having said that, you can click on all white words to make them blue again and create LingQs for them. So, if you are reading, and come across a word you incorrectly marked as known or ignored, just click on it to make it blue.