Believe it or not, sails! Obviously you’re not going to get a 100% reduction because modern shipping companies wouldn’t tolerate being becalmed (and I’m not falling for that article’s “up to 90%” claim either, BTW – I only picked that one to link because it has a decent overview of multiple different technologies), but it can still make a big dent in the fuel requirements.

No. Absolutely not. Sorry, but I cannot this claim seriously at all. We are not going to switch to sail ships again. I don't think you grasp just how big modern shipping actually is, and how impossible such an idea really is.

I doubt you have any grasp of how massive the problem really is, and how tiny your proposed solutions are in comparison. For instance, you keep citing the possibility of using waste cooking oil for biofuels. Well, the world only makes 3.7 billion gallons of that per year: https://oilandenergyonline.com/articles/all/supply-and-demand-report-used-cooking-oil/

Converted to barrels of oil equivalence, that's around 100 million barrels. The problem? That's literally one day's worth of petroleum consumption: https://en.wikipedia.org/wiki/List_of_countries_by_oil_consumption

So you are about 0.3% of the way of solving the problem with that idea. Even if we could radically reduce petroleum use in the way you are imagining, that's still going to be a negligible impact. And the world's GDP is still growing. There's still multiple billions of people that will want to live like the first world. So demand for energy will skyrocket in the coming decades, not decrease. The problem will only get exponentially larger and harder to solve.

Ultimately, this is eco-Ludditism, and is more about wishing away the problem than actually solving it. Worse, you enabling the worse stereotypes about environmentalists. Namely that they are crazy wackos who aren't willing to engage with reality. Any solution must take seriously the idea that there >8 billion people on Earth now, and they all want to live in convenience.