Remove every single package beginning with “pulseaudio”, then install manjaro-pipewire.
I did that recently on a fresh installation, that’s it.
Regarding Jack2 issue, here is below what @philm wrote on the Announcement section :
Pipewire tend to replace all stuff related to Audio. This time jack2 seems to create issues. In the past pipewire-jack provided jack2. However, since the lack of dbus support that line got removed and only conflicts kept. So if you use jack2 with the dbus feature, you may want to remove the pipewire-jack package. If not you can continue and additionally install lib32-pipewire-jack package.
Personally, when i installed manjaro-pipewire after uninstalled all pulseaudio* stuff, jack2 was not replaced by pipewire-jack, and it’s fine for my needs.