Is the video player application itself muted in pipewire? What's the output device set to?

You can check these things with an application like pavucontrol. Pipewire (and pulse) have a default audio device, but individual applications can set a different audio device if they want to.

Another great category of utilities for pipewire is virtual patchbays. If you're looking for something simple, helvum or qpwgraph are geat. For all the technical details in a GUI, coppwr provides a good experience.

I'm not familiar with pipewire, but is there a mixer somewhere in the pipe?

Is the pipewire service enabled for that user? It's a systemd user service

I solved it unistalling it. I didn't want to use pipewire anyway.

I've recently released an Arch package that modifies pipewire to work system wide instead of being bound to the first running user. It's somewhat less secure, which is why distributions don't use this method, but should probably explain the issues your experiencing. Getting it to work properly was quite involved, but pointing your favorite LLM to my repo will probably get you far. Let me know if it helped you.

https://github.com/iddo/pipewire-system