Magnetism is fairly well understood. Gravity, on the other hand, is a very, very big problem in physics. General Relativity, where gravity comes from the warping of spacetime, breaks down at the plank scale. Quantum Mechanics, which typically lives at the plank level, basically treats spacetime as flat and uniform for the sake of math. This results in two separate, very successful theories of physics; one for the very large and one for the very small. Neither theory fits with the other. That's a massive problem. The sneaking suspicion is that quantum mechanics is more fundamental and spacetime are emergent afterthoughts.
String Theory is basically dead. There were some useful mathematical concepts that came from the project but nothing of any substance ever came from it. Most top physicists believe the future is geometric physical theories.
Don't feel bad, Einstein wasn't able to wrap his head around it either. It wasn't until recently that we were able to set up experiments which proved the universe is not locally real (nonlocality) via the 2022 Nobel Prize from a 2016 experiment based on original experiments in the 70's. Einstein insisted that the universe was locally real and there were hidden variables which accounted for entanglement ("spookiness at a distance"). His concept of hidden variables was proven false in these experiments proving that the universe was indeed not locally real.
I think it is easier to start with quantum mechanics and project back to the macro level. If you start with the idea of a singular wave function and only think of "electrons" as manifestations of that wave function, then it becomes easier to conceptualize. The problem is we live in the macro world with macro objects (including ourselves) and conceptualize the world as classically real. If you start to view the macro world through the Everett interpretation of quantum mechanics (many-worlds interpretation), marrying quantum mechanics and your own macro world start to make some sense. There are just a lot of you's in the universe.
Another aspect to bare in mind is the fallibility of your brain. The brain was designed for survival, not truth-seeking. Your brain is literally rendering a mental simulated reality to you on the fly given the inputs from your senses. A simulation machine if you will. From a survival perspective, your brain wants to simulate as fast as it can with the least amount of resources; thus, it is constantly making shortcuts in rendering. This is where optical illusions arise. In the real world, illusions such as bricks being solid when they are 99.9% nothingness or the illusion that you have touched our wife and children (you haven't, the atoms in your fingers or whatever part of your body get close enough to their atoms to repel your atoms and our brain renders that interaction as actually "touching" them). In short, reality is massively different than our mental simulations. Reality is much stranger than the fiction our brains tell us everyday.
A couple things to bare in mind.
1) There is a reason the sighting are mostly off the East and West coast of the US. Those are the best areas for testing black projects. There are no prying eyes there and not singularly located where satellites can easily track. If another country or private-citizen sleuths want to attempt to track these objects moving at insane speeds they have to consider these platforms could be anywhere off our large coasts at night with the black water and the black sky as backdrops respectively. Good luck. Also, since we have our ships on the coast doing training and seas trials, it is a great way to test black projects against the best available white radar and current SOP's.
2) The SR-71, one of the most impressive planes ever, was developed in the 50's by hand. Stealth was developed in the 70's. There hasn't been a fundamentally new technology of air power released since then. DARPA/US Airforce/partnered contractors have only applied and released various platforms incorporating stealth at a rate needed to stay far ahead of the rest of the world. A slow drip of new platforms with analogous perfected technology which serve their function. Yet, the US has dedicated their best minds, best super computers, and virtually limitless budget to creating fundamentally new technology for the past 50 years. It isn't a stretch to think they have some wild prototypes flying around.
3) The platforms don't have a pilot. They are clearly drones which isn't a shock. The B21 can act as a drone as well.
4) I think the splitting in half you are referring to is an optical illusion. You have to keep in mind the laws of conservation.
5) As far NASA, they would have no access to the program. They would be in the dark as much as either of us. These platforms would be of the utmost secrecy due to national security. The benefit of exploring our own solar system would not supersede our national security interests.
6) I would bare in mind that these platforms are obviously moving though spacetime; albeit quite fast through some mechanism of anti-resistance. However fast they may travel relative to our current white technology, they are nowhere near fast enough to explore outside the solar system. The fastest (known) human made object can reach ~500 Mach with the help of the sun's gravity. Light travels at 870,030 Mach. The closest star is 4.2 light-years away. Space in incomprehensibly massive. Aliens simply aren't moving through spacetime.