I've been testing my theory about low volume listening on the open-back headphones (HD595) in the office today. Oddly enough, it's true: it's OK to listen to a very low volume on the headphones. Initially it's obviously too quiet but then my hearing adapts and all is OK, I even had to take my headphones off at certain passages of Shostakovich Fourth to make sure nobody is coming to kill me for annoying them. No, the sound is barely audible by my colleagues. This is an interesting revelation for me, maybe we're too used to listening too loud on headphones and that is bad for our hearing.
Caveat: the above works only in the completely silent office environment and when my colleagues are not in Zoom calls. Once they start speaking or there's any non-silent sound in the room, it masks the music in my headphones. It's an effect similar to seeing in a very dark room. Your eyes eventually adapt, but if there's even slight glaze of light from somewhere, even a bright phone screen, then everything else becomes completely dark.