The moon lander had many complex things, including at the last minute. Remember in space they had to connect up, and separate. Their computer got overloaded when approaching the landing site, and the astronauts had to decide what if anything to do about it. Then they were going to land in a boulder field and the pilot had to take over and go to another place - they had to decide what to do at the last moment. And they almost ran out of fuel before landing (or had little margin left). Each of these things could have lead to loss of the mission.
And neither will Starship when it lands on the moon... it'll do the exact same thing as the LEM. The flip is due to Earth's atmosphere. And there are no runways on Mars, so you can't make a shuttle for it, so you don't have any options left.
What was the backup for landing on the moon? What about Mars?