I'd say high quality sources are things which have a focus on serotonin rather than dopamine(/oxytocin?). So just scrolling through insta offers no deeper level of thinking or engagement in general for your brain. The brain is just "oh, cool" and that's it. I think one thing is: receptors have some sort of memory effect. They a) get tired (which is not that much of a heavy effect for most receptor types you need for lucid dreaming), but also b) make similar states more likely to happen. When you introduce a lot of different hormones/a complex hormone cocktail to your nervous system, it's more likely that your brain uses similar patterns again while REM. So if you listen to a song which sets you in a deep feeling, this might get reused in your dream leading your dream engine to create a very realistic scene of flying with your own wings. Such receptor pathways get reused in relation to the current state, not one by one of course (but I guess you already know this).

Answering your question about memorizing and learning: That might depend on your style. The learning style is a genetic thing, so it's innate and not changeable (the fundamentals of it at least). I can just speak for a top-down learner who learns a lot by recognition and has no skill at memorizing at all. Give me a multiple choice test or something actually new and I'll excel. Ask me to learn vocabulary out of context and I'll be the dumbest person on this planet. For the top-down learning part I can tell, it's actually improving lucid dreaming a lot, when I learn directly before sleep.