It would have a massive effect. Transport (car) emissions are one of the larger - and growing - sources of emissions.
And we can’t hide behind “But the corporations…” because ultimately what they produce gets used by us.
So to answer your question: riding a bike when Global Capital wants you to keep buying cars and pumping oil into them is one of the best acts of defiance you can make
This is greenwashing. Global aviation uses almost 100 billion gallons of fuel per year. If we even began to address a fraction of that with magic new fuels (which won’t happen) it would require incredible amounts of growing, and if we had that sort of amount of agricultural capacity available on this planet, capable of producing crops at a price the aviation industry is prepared to pay, we wouldn’t have any hunger on the world.
Don’t fall for this. There isn’t such a thing as green aviation. I’m not saying there should be no flying, but we can’t carry on as we are and magic away the consequences. In particular, don’t fall for the snake oil salesmen trying to distract you with appealing non-solutions