*Edit: Nevermind, I figured it out. The package name was more specific than what I'm used to downloading through the terminal.*
I'm having the same issue. I'm on Ubuntu but I can't figure out how to install sdl2_mixer. I tried downloading it through the terminal but it's telling me it can't find the package. I might just have the wrong package name but I can't find anything on google. Assuming it can be downloaded through the terminal, what is the correct package name?