"Customer service" is a huge HR buzzword, that's going to be present on just about any job description. As it seems you have already realized, there's no such thing a job that doesn't involve interacting with other people. Something like a librarian should be easy to do. I even worked as a cashier for a while, where I was often the only cashier at the registers.
For me at least, it ended up feeling more like a business interaction than a social interaction. Scan the items, count the money, "Thank you, come again." Very robotic - you go on autopilot after a while. Not much of a chance to mess anything up. They just want to pay and get out of there, and you want them to do the same.
Another job I did that didn't work out was at a call center. That's a completely different context where people are already pissed off about something, which is the reason they are calling. You've got to talk to them extensively about lots of different things, and they are generally trying to get something out of you, and some of them won't leave until they do. Some call centers do provide a script to follow, but the nature of my work didn't allow for a script, so there wasn't that sense of disconnection, of the words to say being planned in advance.
It's all about the context of the interactions.