Maybe all you need to travel from one star to another is just a pair AA batteries, and a 5 min. journey. Hence, very small UFOs would be essentially drones managed from another star.

How could it be possible, well, you have to take a closer look to the probably underlying physics you can infer from the UFOs behavior. Probably the still secret videos from DoD have a lot more to offer than most of the currently available videos.

But for now we have these phenomena reported:
- UFOs can go to full stop instantaneously, even if they are travelling at several times the speed of the sound
- UFOs can go from fully static to several times the speed of the sound, instantaneously.
- UFOs can remain fully stopped, seemingly unamovable, even under a hurricane.
- UFOs can submerge almost instantaneously, almost with no "splash", even if they do at extraordinary velocities.
- UFOs can travel underwater at the speed of the sound, or even more faster.
- UFOs have been reported to go "into mountain bases", decades ago.
- and the most important, UFOs have no apparent source of energy nor thrust, nor anything seeming usable as wings to remain in the air, or some rotors to move underwater.

Then, the physics? The UFOs are probably superdimensional entities / vehicles / vessels.

What we are seeing is maybe a fraction of the actual vessels, most of it located out of our three dimensional space, and you can see "here" is a small sphere of "metal". Maybe this spheres are just small arrays of sensors, from a way bigger unobservable vessel.

The evidence is empirical at most yet, maybe the still secret videos from DoD actually show clearly stuff or moves that reveal the superdimensional features, like a UFO "crashing" into solid rock, just to "re-emerge" from solid ground a couple of miles farther. Or maybe some time-related movements, like appearing / disappearing "from nothing".

If the UFOs are superdimensional capable vehicles, and our three dimensional universe actually has upper dimensions, maybe time itself is a physically traversable dimension, from a hypothetical 5th dimension. Hence, you could actually have FTL - Faster Than Light - travel, but without breaking any physics rules from the three dimensional space. You could be just "fastly walking" a couple of kilometers in maybe 15 minutes in the 5th dimensional space, and you could be displacing yourself several light years in the three dimensional space.

Then the energy required to do a multiple light year travel would be trivial, and the time required to displace yourself in the three dimensional space, too.

You could "jump" from star to star in maybe 5 minutes, using the energy from two AA batteries.

The consequences go far beyond that if the time is a physical dimension: you could go back and forward in time, just like you displace yourself in the three dimensional space. Hence the "time travel" thing remains impossible in three dimensions, but it is easily doable in 5 - or more - dimensions. Even closed loops are possible, because time as physical dimension would imply that "everything is happening at the same time", hence you could travel "backwards" in time and change something, and going back "forward" you'd find some things have changed.

What happens if you can also "travel" in time just as fastly, years in minutes, using just a pair of AA batteries? What if you can go back and change history? You could be changing stuff continously, improving at exponential pace. Maybe the aliens have done so, and they don't have "billions" of years of evolution, but have found a way to make the process faster.

Similarly, the implications of the existence of upper dimensions for the humans in its current level of technological evolution would be amazing. If you can displace solid matter like a plane, using an upper dimension, you could make traverse solid matter in the three dimensional space, maybe even not interacting at all with the solid matter: you could make vehicles capable of travelling throug solid rock mountains, or even traverse across the planet.

Some implications are just wow, if you can travel through solid matter in the three dimensional space or you can build vehicles capable of not interacting with mass in the three dimensional space, automagically most of the weapons and defense systems in the world became meaningless overnight. You could go inside any bank, any militar base, not worrying about missiles, bullets. You can't defend yourself by staying in three dimensional space, but in the upper dimensions you'd can't either: the enemy could travel in time and change its strategy to win this time, they'd just need some observer far away from the theather, assessing if the actions have had success or not, if not, go back, advise and repeat.

So, maybe the "first contact" isn't really the problem, but what happens if humanity suddenly realizes about new, radical advances in physics, available not only to super-powers and super-rich entities, but to anyone with a pair of AA batteries?

Almost no upper echelons of power in anywhere in the world would likely want the entire population know about as radically prone to sudden and profound changes in societies, as a discovery of the existence - and cheap accesibility - of upper dimensions, beyond the three dimensional space.

So you - maybe any super-power, nation states and private groups of powerful people - keep aliens out of sight from the general population, UFOs are psychological operations, not a thing like UFOs actually exist, whatever.

For that reason. You want nothing to change from what it is right now.