Lowest volume when using bluetooth headphone is uncomfortably loud on iPhone & Mac (most likely, iPad as well). I can reduce volume much further on my Android using the same headphones. This only happens when using Apple device with bluetooth headphone and it's been happening since forever. Here're a part of user feedbacks regarding the same issue.
Why is volume so loud? - Apple Community
AirPod Volume too loud at lowest setting ... - Apple Community
lowest volume is too loud - Apple Community
Bluetooth Headphones - Minimum Volume Too... - Apple Community
Bluetooth Headphones too loud at lowest l... - Apple Community
Bluetooth volume too loud - Apple Community
Apple Rant: Bluetooth Volume Too Loud
Bluetooth audio too loud at minimum volume
Anyone else feel Bluetooth volume is too loud even at the lowest setting?
https://twitter.com/sakhtarrrr/status/1265793143330521088?s=21
https://twitter.com/marsylol/status/1013733347888128001?s=21
https://twitter.com/smenor/status/1256254765048098816?s=21
https://twitter.com/appleterminal/status/1280614329038131201?s=21