amix option/command normalize discontinued?
@Gyan in the comments pointed out my ffmpeg version from the Ubuntu apt package manager was out of date. Downloading the latest version from ffmpeg.org/download.html will fix the problem. I'm still a noob regarding Linux stuff... I hope I can somehow declare this ffmpeg version I downloaded from the website in apt because it's always confusing to download many programs and override the package manager, then you forget what you have and where it is. I'll look for a way to do that, package managers are still pretty neat.