In the movies they always show people with Ivy league degrees starting in a mailroom. Is that just a Hollywood thing?

It's mostly a Hollywood thing. Someone working their way up from mailroom to a big job is more dramatic than showing someone uneducated spending their whole life in the mailroom and never getting a promotion and someone else starting their career with a job that requires a college degree.

However, there are probably some prisoners who have Ivy League degrees and work in the prison mailroom. But making the highly educated work in jobs that don't require education is largely a prison thing.

just Hollywood

You're confusing a couple movies about people with degrees starting in mail rooms with the nine million other movies that show people with degrees who have never thought twice about the mail room let alone ever been in one because it's not relevant to the movie or their life.

*Yawn*

Movies very rarely have anything in common with real life. As it happens, mice and other forest creatures refuse to do housework for you, whether you are a princess, or not.