It is more than a matter of rocket engines and fuel. It has to do with a thing called the "rocket equation," which relates the masses required to attain velocity in a single stage, based on the propellant selection. The Apollo solution was a multi-stage vehicle with extremely high-performing propellants in the launch vehicle upper stages. Each stage was drastically smaller as you went up the stack. And nothing much was brought back. Elon has no experience with this approach, and basically his whole SpaceX approach was to take a different path for cheap transportation to orbit. Not by any means a good solution for going to the Moon. His big Booster would make a good first stage, but then he needs upper stages using hydrogen-oxygen propellants and a final stack that is maybe a more modern version of the Service Module, Command Module, and Lunar Excursion Module. But he is planning to use a version of his Starship as the Lunar Excursion Module. That is a huge mass to send to the Moon, thus the fueling penalty for getting it into orbit in the first place.

I did launch vehicle system engineering for a living. I have been following Elon Musk from the beginning. I worked with the people who developed and built the Saturn V first stage. He has the wrong solution to get to the Moon.