Replying to this thread as I was running into a similar issue where many system sources of audio would not play if the Symfonium process was running.
I was able to solve the problem by disabling the Processing Engine in the ‘Equalizer . DSP’ section of the Playback settings.
I’m not sure exactly why this works, it may be a device-specific issue, as it happened on my Motorola Edge (2022), but not on a Galaxy Z Flip 5.