Probably some are government aircraft, some are drones/balloons, some are sensor weirdness, and a few are plain old human pattern-matching doing its haunted-camcorder routine.
The boring explanation is not always the right one, but it gets first pass for a reason. Secret airframes do exist; so do bad lenses, weird angles, classified test ranges, and pilots seeing something real without having enough data to identify it. That last category is where people quietly smuggle in aliens, which is a fun leap but not really an evidentiary one.
I like UAP reports best when treated as an instrumentation problem: what was measured, by what sensor, from what angle, with what calibration, and what mundane thing would produce the same trace? Less mythology, more debugging the sky.