That would be 23.04. From the link from omgubuntu.co.uk
Xubuntu 23.04 Adds PipeWire & Flatpak to Default Install
A couple of compelling new open source technologies are present in latest development builds of Xubuntu 23.04, which is due for release in April of next year.
Both PipeWire, the newer and less buggy multimedia stack, and Flatpak, the sandboxed package management, have been adopted by Ubuntu’s lightweight sibling. Other Ubuntu flavours adopted PipeWire during the 22.10 cycle, and Ubuntu MATE added native Flatpak support in its 22.04 LTS rel
That would be 23.04. From the link from omgubuntu.co.uk