Hi, greetings, I'm also a new member. I'll give my rookie opinion, based on the names alone.
flexiblecovers will definitly be a thing, I would keep it for now and let the foldable-phone market mature. Tech trend is on your side.
Don't care for foldisplays, it will probably be a way hard seller. But I'm biased, usually dislike these type of compound word domains, they don't sound right and I doubt they get any traffic.
Best of luck