OBS seems to capture desktop audio just fine. So its just Steam which has the problem.
The root cause of issue #7833 seems to have effected OBS to and was fixed.
same issue
Distro: Garuda Linux base: Arch Linux
Kernel: 5.15.4-zen1-1-zen
steam build nov 19th 2022
PipeWire v: 0.3.40 running: yes
if i remove pipewire and use PulseAudio everything works fine via Steam Remote Play if i use the default PipeWire v: 0.3.40 then then steam defaults to streaming the microphone even though i don't have one.
Not sure if this is helpful but i managed to get the sound working when i plug in my microphone and launch steam remote play i am able to manually pug in the connections helvum

Issue seems to have been fixed sometime recently. Closing Issue.
Still experiencing this issue, using qpwgraph to manually connect my monitor to steams input. Without this it streams my microphone.
Nothing extracted yet.
Your system information
Please describe your issue in as much detail as possible:
Steam Remote Play streaming Microphone audio instead of Desktop audio on PipeWire Linux.
It is using the Microphone Source instead of the Analog Stereo Monitor Source.
Steps for reproducing this issue:
pipewire-pulse(Basically use pipewire)