Cars are the most familiar to the everyday user, which is why it's the most common in perception. It's also actually one of the easier ones to solve (ie it's basically done).

Trucking is technically not to hard but logistically difficult. Aviation is extremely technically challenging. Shipping is economically difficult. Electricity generation has lots of factors, there's a lot of generation that can and has been changed easily, but some generation which is harder to switch.

If you get outside of oil into CO2 generally, there's even thornier issues. Concrete production, for example.

If you are seriously interested in these issues, I highly recommend https://www.youtube.com/c/EngineeringwithRosie