@freemo To weight in on the whole mumble vs jitsi debate I think you describe two slightly different goals, one better realized with every of those pieces of software.

Mumble is better for permanently hanging out. You can sit there muted and just wait for someone to join. There is a non-intrusive chat which can even be bridged to matrix (although the existing bridges would require some work to provide a nice user experience :/). The sound quality is extremely nice, the desktop client is lightweight, and even when many people attempt to talk at once the quality remains reasonable.

For a quick talk to resolve a discussion face-to-face jitsi is better, because you can actually see the faces (quite important when you want to empathize better). You can also create private rooms very easily and there is good encryption, so anything you say remains private (as long as no other participant records of course). Mumble has private rooms, but they are not intuitive at all. However, sound and video sometimes get desynchronised and laggy, especially under firefox (it's optimized for chrome) or in longer conversations with many people.