Don't know your install, but Debian by default uses Pipewire, not Pulseaudio. If you are using Pipewire, indeed you can't install a Pulseaudio application. That's expected.

You can replace pipewire with pulseaudio. It's doable, just not trivial enough for an HN comment. In general, you'd have to force removal of pipewire without removing all dependent packages, install pulseaudio and then have apt check that all dependencies are ok. Then, having Pulseaudio in the system, you can install paprefs, a Pulseaudio application.

As I said, it's a solid system, rather impossible to break into an unrecoverable state.