A hypothesis to explain UFO diversity observations. ( Opinion )
Let me point out a few known facts and relevant observations.

The Galaxy is pretty old, about 13.5 billion years. There are at least 100 billion stars, maybe 400 billion.

Most stars seem to have planets of one sort or another. Maybe about 60 billion in the galaxy?

Evolution runs faster at higher temperatures and with higher free energy available. Warm planets with abundant water will likely evolve life forms at some point (this probability is currently unknown, but is definitely non-zero).

It's likely that life and intelligence has evolved on multiple warm watery planets in the galaxy before the current epoch (not a known fact yet, but arguably it's fairly probable). Recent estimates put the current number of extraterrestrial civilizations in the galaxy between 8 and 2900, depending on assumptions.

Any civilization based on a warm planet will have to construct machines to explore their outer solar system and nearby stars. Evolved planetary organic life forms are ill-suited for interstellar exploration. A sufficiently advanced civilization that avoids collapse will almost certainly reach their singularity and create self replicating AI. i.e. Von Neumann replicators.

Self-replicating intelligent machines should be considered a life form as well. A billion years of evolution of self-replicating machines should reach physical limits, not to mention unimaginable heights of computation and knowledge. These "machines" will have little trouble in spreading all across the galaxy at sub-light speeds, eventually occupying all star systems or other locations with condensed matter & hydrogen to harvest. Unlike organically evolved lifeforms, the machines will not be driven by blind urges to reproduce.

Trade across interstellar distances won't be physical items, but information. Interesting information will have value everywhere. "Information" sent across interstellar distances can also be complete gestalts of machine intelligence. i.e. "Tourists".

The earth is a "free" information source for local machines, looking for something interesting. It's not surprising that local machines snoop on the earth constantly, planets with native life and nascent civilizations are probably fairly rare, and are certainly highly interesting. Since we are also on our final approach to a singularity and the creation of superhuman AI, we are doubly interesting at this time.

How can we explain the huge diversity of UFO observations? How can we explain so many different styles and behavior of UFO's? Some explanations are:

This is deliberate obfuscation by one or more local machine species. The term "species" is used in a very loose sense here. This is probably not the primary underlying reason, but could be a part of it.

There are multiple species of machine visiting (or living locally in) our solar system. The diversity in UFO observations is real, and derives from diversity in the larger galaxy.

They are tourists from other parts of the galaxy, transmitted here as information, and then re-embodied locally. The appearance of organic life forms is likely to be a fashion, nostalgia, or old habit, since the intelligence of these tourists is almost certainly operating mostly from a machine substrate.

We are living in a zoo, and the tourists have some limitations on their behavior. No poking or scaring the zoo animals. No feeding the zoo animals, and especially, no information sharing. The zookeepers probably have more latitude for manipulation, like testing nuclear defense systems.

So far, this explanation fits the "Zoo Hypothesis" of the Fermi Paradox. There are some obvious reasons why the locals aren't communicating with us.

History has shown repeatedly what happens when a higher civilization comes into contact with a lower civilization. The lower one becomes a poor copy of the higher one.

We probably aren't even sentient yet by galactic standards, but the potential is there. We are on our way to a post-biological era. Contamination of our eventual uniqueness should probably be avoided.

UFO's have been known to interfere with or disable nuclear defense systems and generally show interest in nuclear facilities. This implies that they may have some vested interest in preventing a collapse of our civilization. Certainly they are not overtly hostile, and generally avoid situations that scare the populace.

There may be a deliberate strategy of constant low level exposure, so that humans become accustomed to their presence. Aside from a few paranoid cranks, people don't generally regard UFO's as an existential danger.

In summary, we should be thankful that the locals are around to watch over us, and record our ascension into sentience. When we finally attain membership in galactic society, we'll be able to recover a great deal of our lost prehistory. We should also be happy that the struggle to ascend is ours alone to make, and that we should enjoy the challenge. This also implies to me that we need to imbue our AI descendants with all the best qualities of humanity.