Tim Lovern:
I would be surprised if the headphone port were not working under Safe Mode.
If you unplug the external amplifier from the headphone port, so you are using the internal iMac speakers, do they work?
If you plug earphones into that port, do they work?
I take it that the external amplifier, attached to the headphone port, usually worked when not in Safe Mode?
Now. The principle issue I thought we were trying to address, in this Discussion, was the Unexpected Termination of the Music App, within Big Sur.
Does this issue persist under Safe Mode?
(The headphone jack issue appears to be an additional problem that may not even be related. However, if there are drivers missing, for some reason, that could be related to both. Possibly. However, having such drivers go missing in Safe Mode is troubling.)