Came across this video on YouTube researching science and technology called, Aerogel - The Secret Link. The title is all click-baity, but I checked it out, and apart from a few over-excited extrapolations I think they're basically right.
I've known about aerogel for a while. It's a proposed material for deep space particle protection along with Whipple Shields. I'm a science nerd, bite me.
Anyway, I followed the links: Light-induced levitation of ultralight carbon aerogels via temperature control, Layered shell vacuum balloons, which are just ways of making a vacuum airship/balloon, that uses the fact that a vacuum is lighter than air instead of a lighter-than-air gas.
Below is a screen capture from the second link.
The problem up to now is how to make a balloon that is light, yet strong enough to resist being crushed by the air pressure?
My position on the whole UFO/UAP hysteria is that these are secret projects. YMMV