This excerpt from the Police guide is interesting. They are discovering more of these craft after "removing Cold war-era filters from radar".

Whereas the Chinese spy balloon was visible to civilians from the ground, the three other objects shot down by American fighters over Alaska, Canada, and Michigan the following weekend were only detected after the North American Aerospace Defense Command removed Cold War-era filters from its radar. Previously, filters excluded anything too small, too high, too slow, or too fast to be a Soviet bomber or ballistic missile.

This is not the first time that upgrades to our sensor capabilities revealed unidentified phenomena in our skies. In 2014, when I served in the U.S. Navy, my F/A-18 squadron and I were operating in a military training range off the coast of Virginia and began witnessing unidentified aerial phenomena (UAP) on radar and infrared after a generational upgrade to our systems. My squadron then started seeing them with their own eyes, including a dramatic near-miss.

The shootdowns last February marked the first time in the 50-year history of NORAD that fighters destroyed objects in our airspace

https://majorcitieschiefs.com/wp-content/uploads/2024/06/MCCA-UAP_Reference-Guide-June-2024-.pdf