The core problem is that humans (and most other living things on earth) evolved to live in a certain climate. For each organism, the tolerance for change differs. If we lose an intolerant, important organism (let's say plankton, for example) and it goes extinct, then there's a chain reaction that ends up making the planet uninhabitable for us.
> Are the apocalyptic warnings anywhere close to reality?
It depends on the warning. Will human life on earth end in 10 or 50 years? Probably not. But will we have a mass migration crisis that will threaten every wealthy country? Yes, and it will happen in less than 50 years as natural disasters and poor crop output drive people from their birth countries.
Climate models from Exxon and public-sector scientists have been pretty accurate at describing the current state of our climate, so predictions from sober, professional scientists are worth paying attention to.
The rest of your arguments fall into a few categories:
A) Attacking a straw man. No one seriously things that going meatless would instantly solve the problem. There is no single solution. It requires many large changes to small aspects of our lifestyles. Eating less meat (not zero meat) for people who can afford it is helpful.
There is a helpful list and rank of different approaches[1].
B) "Green energy (excluding nuclear) is too expensive and can't compete with fossil fuels in an open market." This is not true[2].
C) "Nuclear must be part of the answer." I think this might be true or might not. It's another huge prediction, isn't it? Why are you skeptical of some predictions about 2050, but not others?
D) "Celebrities are hypocrites." Yes, they are. But it has nothing to do with the argument environmentalists are making. I find them irritating too, but it doesn't make environmental concerns any less reasonable. Celebrities are a tiny fraction of environmentalists.
E) "Taxes are bad." Taxes in the US have rapidly gone down in the last few decades, but increasing them is a separate argument from the environment. Taxing carbon producers is a serious proposal, but that's not taxing Gates or Bezos -- it's forcing companies to pay for the damage they do to the air and environment the rest of us need to survive.
1. https://www.drawdown.org/solutions-summary-by-rank
2. https://www.forbes.com/sites/dominicdudley/2019/05/29/renewa...