Luis Elizondo, former head of the Pentagon's Advanced Aerospace Threat Identification Program, has publicly stated that they're 99% sure that the 5-10% of the crafts they are not able to identify are not technologies from foreign governments. He's also mentioned that the Pentagon is aware that Russian and Chinese governments are also in the same position and have been working to figure it out.

These craft pull 500-800Gs and have been measured to be going 13000-20000mph+, so it's highly unlikely that they're made by humans, unless we've figured out a way to not turn into goo at that force, and use materials that could withstand that force as well.

Whatever these things are, they're not weather phenomena, nor illusions, especially when they've been visually identified by countless navy and air force pilots, and picked up/measured by military radar, satellite systems, and other instruments. Pretty sure the military would have easily ruled out weather phenomena/illusions given their budget and capabilities.