Okay, I think I have finally spotted theroot cause. # drwxr-xr-x 2 pipewire nogroup 120 24 sept. 21:31 /var/run/pipewire//
And indeed, /usr/lib/systemd/system/pipewire.service which defines this directory does specify to which group it belongs. We have: User=pipewire but no Group= line. Adding Group=pipewire just below the previous line fixes the issue, after a reboot or restart of the associated service.
