If it's drones (which is laughable if you think logically about it) then handful of them were literally purposely destroyed going into the water....
They already make simple-ass drones that can both fly through the air and navigate underwater, but you don't think the world's militaries have that technology?
While aerial drones can travel long distances quickly, aquatic drones can explore underwater environments. The TJ-FlyingFish offers the best of both worlds, as it's a flying quadcopter that is also able to make its way through the inky depths.
newatlas.com
When the aircraft is in flight, all four of the units are facing upwards and spinning their props at the higher of the two speeds. Once it lands on the water, the units rotate to face downward and then spin at the lower speed, pulling the drone beneath the surface. In order to move both vertically and horizontally once it's fully submerged, the drone adjusts the angle and thrust of each propulsion unit as needed.
And yes, once it's done with being underwater, the drone can go back to the surface and fly away.
But honestly, I'm doubtful of most of the claims about UAPs flying underwater, because the only videos I've seen where they were supposedly doing that, it was clearly an optical illusion based on poor video resolution followed by an overactive compression algorithm, and in reality it was just flying with the water in the background the whole time.
Over the course of multiple days... Off into the ocean.... If it's balloons then they're debris should have easily been identified and salvaged after it touched down in water and multiple ships investigated the "touch down". If it's either of those things then there is an obvious problem with our military tech being unable to identify rudimentary equipment so that's a problem as well.
Yes, it is clear there are a LOT of problems with our military being able to deal with simple-ass drone shyt. You see that all over the world. That doesn't make them UFOs.
But I also think you're badly underestimating how difficult it is to find shyt in the water. Sailors on Navy ships have fallen overboard and failed to be found on multiple occasions, even though they fell right next to the fukking ship. Something floating on the surface is hard to find, something that sinks below the surface is damn near impossible to find.
We also don't know how much has been identified, but is being kept secret from the public (and even from other parts of the military, for operational security), because the Pentagon doesn't want other nations to know what we actually have, or know how much we know about what they have. For all you know, they recovered lots of these drones, but are purposely pretending that they didn't because they don't want China/Russia to know that we've got their material and are analyzing it.