Good questions. I will answer as numbered.

1. By doing nothing, Trump left big tech constrained by rule of law. For example big tech's recent attack on Parler is a blatant violation of antitrust law. This wasn't possible under Trump. Big tech is threatened by the free market. Their software is decaying and they are out of touch with consumers, so alt-tech and other companies are threats. So they want to use the government to take complete control. Also, taking over the government generally increases their power, and power is their goal. Even during Trump, they were able to buy most of Congress but they couldn't buy Trump.
2. This may be hard for a European to see, but to the average American Hillary Clinton had much more charisma in 2016 than Biden has now. She wasn't senile and she actively campaigned. In this election, BLM also helped Trump in the Rust Belt states. The Democrats weren't so obviously hostile to middle America in 2016.
3. Reality is generally irrelevant in America. The reality of Biden's record is that he never actively supported leftist causes. He was basically just completely corrupt and served corporate interests, particularly credit card companies. He was tough on crime because that got him votes in the past. Nothing that he said in this campaign is supported by his voting record.
4. The courts are part of the political class and all of the political class abandoned Trump. And for good reason. Trump is a pathological liar. The only people stupid enough to believe Trump are the moronic masses on the right. The political class knows that everything that Trump says is worthless. So Trump's promises of support are worthless and Trump's threats can be ignored. In contrast, the threats from the globalists (big tech, Soros, etc.) are very real. Any action against the globalists means a serious attack on one's political career. So this is why the entire political class, including the courts, abandoned Trump.

In Trump's phone call to Georgia officials, Trump was just alluding to the kind of evidence Giuliani talked about. I used to ignore conspiracy theories, but now the globalist conspiracy for the great reset is in plain sight. Big tech is part of that conspiracy because the basic point of the whole thing is for the upper class to take complete control and reduce the rest of the world to serfdom, and this certainly appeals to big tech.