Pipewire replacing PulseAudio was not a decision made by Manjaro
Users who had Pulseeffects installed would have been asked to remove PulseAudio,
because the Pulseeffects developer changed the dependencies to require the change
One of the Manjaro Team recently quoted one of my posts about using PulseAudio
and a post from another user about using Pipewire
Failed update due to pulseaudio dependencies - #2 by bogdancovaciu
One of the early posts after the update had this expert opinion
PulseEffects issues with Pipewire - #4 by mr_glitch
And that discussion also has later posts by another user about use of Pipewire on KDE
If the KDE volume controls are not working correctly, you could try installing pavucontrol-qt
I have also seen comments that pamixer works with pipewire
One thing I was not aware of in previous discussions about pipewire is that there is more than one systemd service. I only found out 2 days ago that there is a pipewire-pulse.service in addition to pipewire.service
So on your system, if you check the systemd units
systemctl --user list-unit-files | grep pipewire
You should see this if both services are active
pipewire-pulse.service disabled enabled
pipewire.service disabled enabled
pipewire-pulse.socket enabled enabled
pipewire.socket enabled enabled