Anecdotal, but every single person I've spoken to who voted for Trump does believe one or more of these conspiracy theories.
I've found that the most reasonable people tend to be staunchly pro life. And I can see that—if you truly believed abortion was murder, it would be reasonable to support almost anyone who might stop it. I don't believe that, but I can respect it. Others tend to believe things about the world that I don't think are true, like climate change isn't a big deal, other countries have been taking advantage of the US for decades, democrats are controlled by the military-industrial complex, etc. Their conclusions might be reasonable if you take their beliefs as fact, but I think their starting position is flawed.
And then there are of course those who aren't reasonable. Those who just enjoy watching Trump troll libs. Those who want to see the whole system burn. Those who just believe whatever Fox or Breitbart or whatever says. Etc.
I mean, I'm sure I have my own biases. I despise the very thought of the man, because of the way he acts and how he doesn't care about the damage he does. But I'm sure that feeling makes it difficult for me to see any of his positive qualities, or that someone could (perhaps rationally?) value those qualities over the negative ones I see. So far though, I haven't been able to find evidence to change my mind.
For example, suppose a person doesn't want to become a linguistic or religious minority in their own country. When they logically oppose immigration, do you decide that you're hearing a dogwhistle for white supremacy? If so, you're discarding what was actually said and you're substituting false data that supports a pre-determined conclusion that Trump supporters are racist.
Another factor is that there has been some truly shocking projection and gaslighting with regard to corruption. Like no other president, Trump has fought corruption, yet he is relentlessly accused of it. The claim that Obama had a "scandal-free presidency" is a cruel joke; his abuse of the intelligence apparatus to target a political opponent made Nixon look saintly. Biden's family has gotten rich off of foreign influence; we have the evidence and there is no alternative explanation. The whole impeachment process started because both Biden and Pelosi had children collecting bribes from Ukranian gas companies, and Trump dared to tell the Ukraine that prosecuting the corrupt was proper. Looking back to Hillary, her actions with classified information would have put any normal person in prison for decades. The contrast with Trump is stunning. For years everybody has investigated Trump in hope of finding something, and everybody has failed.
The desire to put America first is real, legitimate, and proper. It's a job requirement for the president.
Cutting regulations shot the economy to record highs before that virus hit. Inequality actually dropped. Black and hispanic unemployment was the lowest recorded ever, with records going back over half a century. Trump knew what business needed, and he delivered.
Why do you imagine that "he doesn't care about the damage he does"? He is only damaging things that need to be damaged, like the choking bureaucracy. He cares, and he did the damage on purpose, because the damage was needed. If by "damage" you're referring to something like the opinions of the leftist leaders of parasitic countries, yeah he doesn't care and he shouldn't care. The job is to put America first, not to please foreigners.
And to answer your final question, the most recent example of Trump not caring about the damage he does is him currently undermining faith in the democratic process itself in order to avoid admitting defeat. More generally, he will always take opportunities to fire up his base despite any deleterious effects on national unity. And yes, also his actions and rhetoric toward strong allies such as Canada. Framing such as "parasitic countries" is both inaccurate and diplomatically unproductive - from you, but especially from a world leader. I would go further into why I disagree with that approach, but that would lead me into all the things I disagree with here. So instead I'll just ask you to do some research on your other points outside of right-wing sources. The most clear-cut one is this thing about Pelosi's son, so maybe start there.
Other aspects of culture matter too. It's just more comfortable to know that your neighbors laugh at the same jokes, celebrate the same holidays, and so on. People who want different can leave, but people who want the same have no option other than to fight to keep their culture from being overrun.
This idea that there is a problem with "undermining faith in the democratic process itself" suggests that the most important thing in a fraudulent election is to hide the flaws. I hope you were at least fair about that, not complaining at all when Trump or Bush won. I hope you opposed taking those elections to the supreme court. Lots of people claimed that those three elections were stolen, and lots of people even rioted. If you had any complaints whatsoever about those far-cleaner elections, you're just being partisan. I happen to believe that there is a duty to expose problems, including any way by which fraud could go undetected. We shouldn't just trust that an election could be clean; it is dirty until proven clean. The fact that the left has vigorously opposed election integrity efforts is shameful and highly suspicious. If you'd rather Trump didn't have a legitimate argument that the election was stolen, maybe you should have cooperated in securing it against all possible fraud.
Have you found the perhaps-mythical unbiased news source? Are there any non-right-wing sources that don't censor the news and maliciously spread misinformation? Anything that spread the Russia hoax or "fine people" hoax is disqualified immediately. If the news source didn't fully cover the Biden laptop, it is censored. Full coverage includes at least a description of where to find the video of Hunter naked and worse with his niece, and it includes mention of the email being DKIM verified. The news is censored if it didn't included coverage of Biden's sundowning and other signs of dementia. The news is censored if it never tied the Ukraine controversy back to Joe Biden being caught on video bragging about how he got the Ukrainian prosecutor fired by threatening to block a billion dollars of foreign aid.
The purpose of an open mind is to close on the truth, but that should be more like science than dogma. New information can change conclusions.
My value system is largely focused on the success of my descendants, including distant ones not yet born. They will prosper best if they have complete dominance for their country, culture, language, and religion. They are more likely to die off otherwise. To prosper they also must avoid the mistake of leftist government (socialism, communism, etc.) because that killed over 100 million people in the 20th century and it's still killing people today.
Answering a couple more points from your original comment here: I don't just enjoy watching Trump troll libs, but I do enjoy it. There is nothing wrong with a bit of fun. People on the right don't believe Fox anymore, and haven't for several years. There was an ownership and control change, with Roger Ailes dead and Rupert Murdoch mostly gone. Aside from two major commentary/interview shows, Fox is now leftist. Fox even hired Donna Brazile, the disgraced former head of the Democratic National Committee.
You mention that you despise the very thought of Trump because of the way he acts and how he doesn't care about the damage he does. OK, so what about that crime bill? I mean the one that put lots of black people in prison for crack. Joe Biden fought hard to pass it, Kamala Harris eagerly used it to put black people in prison with huge sentences, Hunter Biden was immune from it while smoking crack, and Donald Trump signed a prison reform law to stop the harm. How can you not despise the very thought of Biden because of the way he acts and how he doesn't care about the damage he does?
As you say, "I'd really like to understand how reasonable, ethical people could vote for someone I see as so despicable and dangerous." Yes, me too, but the other way. The 100 million are dead, and more are dying. The war in Iraq, supported by Biden, killed plenty. A few decades of life in prison is roughly equivalent to a death, and there were an awful lot of those. Perhaps you can explain why all these things are reasonable and ethical?