I have the same problem.
Supposedly genuine Airpod Pros purchased within the last month from an authorized retailer (not the Apple store). They show "Spatial Audio Not Available" on my 14" 2021 Macbook Pro (MacOS 12.1) AND iPhone 12 Pro Max (iOS 15.2). The firmware on the Airpod Pro is set to the latest release (4C165). There is no reason this shouldn't be working, but it is not.
When I run the test inside the Airpod Pro menu via Bluetooth settings on my iPhone, it acts as if it's playing but I hear no difference. At this point, I believe the Airpod Pro's are defective as are a meaningful percentage of others.
I suspect Apple knows this, their reliability engineering team always does. Whether they acknowledge it and offer a replacement/fix is another story, but I'm not getting my hopes up. In the meantime, I'll be pushing on my Apple Care coverage and Apple Support for a resolution.