the “Default Startup Volume” gets ignored/not activated in “Playback Options” -> “Mixer = Hardware”.
The “Default Startup Volume” can be set (and saved) to eg. 10% but after a “System Restart” the “old” volume value is this in place and visible in Web-GUI. Probably the “Default Startup Volume” is actually “set” but just “not activated” because when touching “up/down” Volume the “Default Startup Volume” is used as the “reference / starting point” for the volume change.
The problem is when using active spakers directly behind a DAC the “Default Startup Volume” should be very low for not to damage the speakers.
Version v2.806/v2.824 (sereval different installations whith different Pi3/4) and different DACs (I2C, USB).
kind regards and greets