"The sightings always recede to the edge of what technology allows you to do," Shostak told Space.com in 2019. "The aliens are kind of keeping pace with technology."
This is a bad bit of reasoning. That "edge of what technology allows you to do" is a horizon beyond which we have no depth perception. Anything beyond that horizon seems equally impossible. To put it more plainly:
Group A is 1,000 years more advanced than Group C. Group B is 100 years more advanced than Group C.
At a single glance by Group C, both A and B seem equally impossible, because everything that exists beyond the horizon of their own technological abilities just seems like magic.
So the fact that UAP always seem just beyond the horizon of our technological abilities isn't due to the fact that UAP are constantly adapting to be just one imagined step ahead of our current abilities. It's due to Asimov's law that any sufficiently advanced technology is indistinguishable from magic. And all magic, by its very nature, seems equally magical.