How to fix sound device switch bug in Ubuntu MATE 19.10?
This is a quite an annoying bug at the moment on Ubuntu MATE. When you have more than one sound device in your system, and you want to switch to the preferred one, it doesn't save it, and when you reboot your machine it switches back to the other device.
I have found a simple solution for this. We need the PulseAudio Volume Control program. Just search and install the pavucontrol package:
sudo apt install pavucontrol
Start it from the menu, and go to Configuration tab, and simple turn off the device. It will save it properly and you will have no problem after reboots.