Hmm, it looks like the first few messages there are doing initial setup. After that, it looks like it’s having trouble loading some of its libraries. Then it isn’t able to read your sound devices. I haven’t run Mixxx with nixos or pipewire, but maybe try the flatpak? Sorry it isn’t running out of the box for you.
Glad to hear it! Mixxx has been one of my favorite projects to use, and they always surprise me with new features whenever I open it up!