Yes - my system is working now.
it wasn’t after even after deleting the symbolic links in ~/.config/systemd/user/ mentioned above but after systemctl --user restart wireplumber, the following ran perfectly (and no files that I’d deleted were recreated ~/.config/systemd/user):
● Audio --aid=1 (mp3 2ch 48000 Hz 133 kbps)
AO: [pipewire] 48000Hz stereo 2ch floatp
A: 00:00:04 / 00:03:45 (2%)
and this appears to have been with the nixpkgs-unstable and nixos-unstable-small packages that were already installed as the nixpkgs-25.05-darwin/nixos-25.05-small had been failing to build with some overlays I was using in a length overlays.nix file referenced in configuration.nix.
I just completed a nixos-rebuild switch back with nixpkgs-unstable and nixos-unstable-small that lasted <10 seconds after typing this and will likely reboot soon
**
Bluetooth is working now as well; so this is resolved, although I’d like to keep this thread open a bit longer to hear any input @PlasmaPower might have about what exactly wireplumber did here and how the steps taken in this thread actually allowed my system to regain audio and bluetooth function