Are there any alternatives to Window 10 out there?

[aFarewellToKings]

I need to learn Linux a bit, CentOS specifically. I was thinking to get a Raspberry Pi and load it on there. Does that seem reasonable? I am not a computer enthusiast.

Just use Raspbian, it works great. Why CentOS? Under the hood they are probably similar, it's just the gui that's different.

I have to use CentOS for some work stuff. As long as commands in terminal are the same it should be okay. I think.

CentOS is basically Red Hat (the free equivalent to the supported, paid, Red Hat).
The main difference would be the set up and configuration tools. Red Hat has their own stuff for that. But Raspberry Pi is ARM, not x86, so much of that would be different anyway.
Command line, and even GUI and apps, would be mostly the same.

Maybe the biggest difference you'd see would be the app search/install/config system. Red Hat uses rpm, whereas Raspian uses apt. Besides file formats and maybe some minor differences, they are equivalent. Although I believe you could use either on either.