I don’t see any plausible options, but would note the US has never run ops like this. Keep in mind the US has lots of emptyish desert to test over, and the American doctrine of tech development has always been to claim to have less technical advantage than it really has, as compared to most nations and the old USSR, who claim to have more technical advantage than they actually have. It is not in accord with standing doctrine to showcase technical ability in the way you are suggesting.
Recall for example the US was operationally flying the F117 for more than a decade before anyone had ever seen one, and Bill Clinton took huge grief for revealing that program by finally forcing them to fly in daylight during the war in Kosovo. There is huge value in revealing tech advantage, but you only get to cash in like that once and a lot of people thought Clinton should not have revealed that program, but merely just used it at night the way it was designed.
So, to put things in proper context, the F-47b carrier based attack drone was tested aboard aircraft carriers over a decade ago, then publicly retired, despite Northrop-Grumman built an expensive composite wet filament winding gantry that could supposedly mass produce 47b airframes for less than $10k each on a daily basis.
So what do you think actually happened to that airframe?
The US always keeps its cards close to the chest. It appears to me US low tech quadcopter drones, helicopters and fighters are all being used to chase these “orbs” and the orbs are here simply to demonstrate they can be here.
As to the current rumors of “smart dust”, those items are 1mm on a side. If they were the stuff of fog we would all know. The fog is something else. Much of the fog is just fog. Reports from Oregon of “mysterious fog” are likely hysteria. Oregon gets lots of fog this time of year. (I know because I lived there for 12 years and I am allergic to the mold and mildew in the air 6 months out of every year.) Vids of Oregon fog show wet roads as you’d expect.
OTOH, the reports of dry fog from around the world and chemical residue in pools and on sidewalks—that seems an authentic mystery even if it is based upon false reporting as part of a psyop. US DoD is no stranger to running psyops on its own people. No news media have reported on foamy chemicals in people’s swimming pools and I have seen zero chemical analysis of the stuff these dubious vids are reporting. So far looks like a psyop to me, or perhaps even just malicious pranks. People are turning that creepy, that you’re forced to wonder.