Why can't I change the default output sound device on Ubuntu 20.10?

Today I struggled with an annoying issue concerning the sound system on my Dell XPS 13 7390. Ignoring whatever output sound device I selected, Ubuntu would instead play the audio directly through the built-in speakers. To quote what I regularly hear from my users, “it worked yesterday, and I didn’t change a thing!”

Microsoft Teams for Linux won't open on Ubuntu 18.04

After installing and running Microsoft Teams for Linux on Ubuntu 18.04 for a couple of days, the application suddenly stopped working. Starting Microsoft Teams would load the application menu in the top bar, but it was not possible to get the actual application window to load. Clicking “Open” from the application context menu would do nothing at all.