I have a Mac Mini 2018 that I sometimes connect my headphones to. They work just fine. No issues with volume.
But if I connect the Mac Mini to a receiver (a Denon AVR-2106) via the minijack with a 3.5mm to RCA cable, then the volume on the speakers connected to the Denon is too low.
The volume on the Denon is in dB and starts in negative number (never understood why) and I have to crank it up to 0db and then I can barely hear the audio from the speakers. Also, I have to max the output volume setting on the Mac.