Hello @Kwjj ,
To rule out any physical damage to the volume down button, I recommend testing whether holding down both the volume down and power buttons simultaneously works for you. Does this combination bring up the power-off menu or take a screenshot (depending on your settings) without any issues?
If the problem isn't hardware-related, I suggest submitting an error report through the Samsung Members app. This will allow our developers to investigate the issue in more detail. Please make sure to specify whether the volume down function is unresponsive across all apps or just within a specific one.
Have a great day!
