You could replace mate-volume control applet with the pnmixer.
sudo apt install pnmixer -y
In the Startup Aplications find the Volume Control
and replace mate-volume-control-applet command with pnmixer.
Log out and back in and you’ll see that the icon changed.
Right click on the tray icon -> Prevferences -> Behaviour tab
In the Volume Control Command text box type in
mate-volume-control
Go to View tab and select the slider orientation. In the same tab you can set the volume meter and volume meter color. Offset 1000 %. If I enable “Use System Theme” icon is buggy for me.
You can set the hotkeys in the Hotkeys tab and in the Notification tab you can enable notifications.
What pnmixer doesn’t show is decibels in the tooltips, but the middle click mutes volume and mouse scroll changes volume.