Ends up clear cutting the rainforest to grow more soybeans, and there is nowhere near enough used vegetable oil for use at scale.

Luckily EVs and high efficiency internal combustion vehicles are driving down the demand for ethanol in the US and obviating the need to consider biofuels as a petroleum alternative.

Depends on the source of course. McDonalds in the UK claim to fuel about half their fleet of delivery vehicle with the used oil from their own restaurants.

If you get the source right, biofuels are great. But as you say, get it wrong (e.g. the EU policy of encouraging bioethanol) and it is disastrous for biodiversity.

I'm surprised we are not doing more with sewage, but I suspect that is to do with the difficulty of processing such a mixed substance, and the amount of infrastructure that would have to be changed.

I’m familiar with efforts to use sewage and landfill gas for small scale fleet fueling needs (local municipality and garbage collection vehicles), I just don’t think it scales up much beyond that.

I have to agree with @toomuchtodo -- the "bio" part gets gamed by the industry.

That said, I own a "biodiesel" vehicle and hope to find the time and opportunity to actually make my own fuel.