How could an audio player does not have volume control button nowadays? Yes, Rhythmbox does not have it out-of-the-box in my Linux laptop!
If you have the same problem, this simple tutorial may help!
1.) Firstly open the music player, and go to upper-right corner app menu, then click on “Preferences.”
2.) When the Preferences dialog opens, navigate to the Plugins tab. There enable and go to the ‘Preferences’ for Alternative Toolbar plugin.
3.) Next you’ll see the option for “Volume Control”. Just tick the check-box to enable it, and click ‘Restart’ button to apply change.
Finally, you’ll see the volume control button on the right side of the toolbar.
That’s it. Enjoy!