If it's stuck at max, then Pipewire isn't controlling it. Try alsamixer as a different test, or maybe qasmixer. You'll need to select the hardware id for the device to try and change it.
You might want to dig around keyword searches for your specific model and "Pipewire" to see if others have a config to sort it if the above works.
Looking up the hardware id, it seems that someone else had the same issue: https://github.com/alsa-project/alsa-lib/issues/401
If I'm understanding correctly, there's no proper driver for it in the kernel yet. My workaround for now is to use the limiter in pulseeffects.
Edit: If anyone wants to know, it does work flawlessly on Android, but I have no idea if the way Android handles USB audio is relevant to desktop Linux at all.
Good find, but it's not a kernel issue in this case. The device is recognized as "something", and outputs audio correctly, you just need to find out where it's getting it's audio from, and assign a control channel through Pipewire to control the sink volume. Should be pretty easy, but will require some digging and a quick bit of learning.
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