This looks to be an earlier version of the new Android Material 3 volume bar. The three dots brings up a UI to let the user change the mix of all the channels (music, alarms, ring, etc.). My current updated AOSP phone shows the three dots outside the bar that shows the current volume (colored with the accent color). This one shows it inside. It seems this user’s accent color is beige.

Edit: Maybe it isn’t so old. See https://infosec.pub/post/36886556