Sound input/output selector indicator for Linux.

This app shows an icon in the indicator area or the system tray (whatever is available in your desktop environment). Icon’s menu allows you to switch the current sound input and output (i.e. source and sink in PulseAudio’s terms, respectively) ports with just two clicks.

https://yktoo.com/en/software/sound-switcher-indicator/#installation

sudo apt-add-repository ppa:yktooo/ppa
sudo apt-get update
sudo apt-get install indicator-sound-switcher

Start once

Other options via scripts:
https://forums.linuxmint.com/viewtopic.php?t=236439