Same here! So frustrating, because I like the convenience of carrying a library of music with me. Whether I plug my Xperia XA-2 into headphones, a portable speaker, or a HiFi, the volume is way too low, also after dismissing the audio level warning (by clicking “yes, I understand”) and turning it up to the max. This cannot be right.
Edit: I’m currently on Sailfish OS 4.1, but this issue was present also in earlier versions.