Hi Fidelity Playback vs. Headset Head unit is the difference.
Bluetooth doesn’t provide enough bandwidth to handle both input and output, so when the mic is used, the headset head unit is selected automatically to reduce the audio output’s quality to accommodate the mic’s bandwidth needs.
That’s ultimately the issue - as you can see with your change of input device in Discord. Removing the mic input lets you use the high-fidelity output option.