I know aviation and weather professionally and have yet to see a credible, visual UFO claim from the last half century that could possibly be explained by “clutter” like a weather balloon.
The word clutter does on rare occasion reasonably get used by air route traffic control types in reference to what sometimes appears on their monochromatic radar scopes, which almost never depict such things more than two-dimensionally.
How about the clutter that you see in IR systems, which happens all the time? People who think these Navy FLIR videos are showing something amazing have never seen F-18s and other conventional aircraft in IR.