The arts are probably one area in general where it's mostly impractical to show up at college, decide this thing is really cool, and decide to make a career out of it--over and above the lottery nature of the field generally.

Arguably there are some aspects of this in software as well--deliberately avoiding the CS term--but it's almost certainly going to be really hard for someone with no music background to show up at university and decide this is something they're really interested in.

At a first or second tier school, it would be basically unthinkable. None of the professors would even be willing to give you lessons -- they fill their studios through the audition process. It would be a huge waste of money to pay college tuition for remedial music lessons. Also, a big part of college music study is playing in ensembles that are coached by faculty. You have to be at a level where you can hold your own in an ensemble or you can't even participate. The schools are careful to admit only those students who can hang in the ensembles. Getting into music school is an application process on top of getting into the college.

With that said, you could get lessons from a graduate student who wants to earn some money.

My observation (two kids in music school) is that undergrad music is almost like grad school in other fields, in that you sign up with a specific professor who is your teacher for 4 years, and their job is to turn you into a fully fledged professional. The kids who are coming out of those programs are ready to start an independent professional career, the only obstacle being competition and not competence. My daughter, who is graduating this spring, is in fact playing professionally.

(At a tech school) I signed up early-on for an Intro to Music course I thought would be interesting--and to be clear it was. But as it turned out the person teaching the class was a pretty well-known choral director (John Oliver as I recall) and pretty much everyone else in the class were well-versed in music and were there because of said well-known choral director so not knowing the difference between major and minor keys wasn't really part of the program.

It was fine. It just wasn't really what I signed up for.