Did Ubuntu choose WirePlumber or `pipewire-media-session`?
Arch tried to switch off from `pipewire-media-session`, because it's merely a proof of concept whose development is dead, but found that WirePlumber simply isn't ready yet (https://archlinux.org/news/undone-replacement-of-pipewire-me...).
It seems like, unless and until WirePlumber is actually ready, PipeWire isn't quite ready?