How common are large student loans, and how do people get a degree?

Hi all, I live in Europe but am a US citizen, and can't afford to go to the states for an in-person college tuition. But I plan on moving back in the future.

How normal is it to accumulate large sums of student loans? I've heard of people taking out 100k loans, but to be honest that really scares me. I couldn't imagine going to the states, and taking out a 40.000 dollar loan. How do yall get an education if you want to become a doctor for example?