Hey Dominique!
We're glad to hear you were able to work with Blue regarding your microphone. We understand the LED is on, and that Blue indicates the microphone is getting enough power when the LED is on. Did you have a chance to confirm that the USB-C adapter provides enough power to allow the microphone to be recognized when connected? We want to be sure since their article on what to do if My Blue USB mic won't turn on indicates you should use a 1 to 1 adapter.
In regards to the listed Technical Specifications and System Requirements for your Blue microphone, we'd recommend working with Blue directly to confirm compatibility, and if needed, ask about updating the information provided.
We can tell you that not all third-party accessories are compatible with all Apple devices and adapters. If you've had a chance to go through the steps on what to do if you see an 'Accessory may not be supported' alert and the microphone still isn't recognized when using the USB-C adapter with your fourth-generation iPad Air, we'd recommend confirming the microphone is compatible.
If it is compatible with the fourth-generation iPad Air running the latest version of iPadOS, we'd recommend trying a different adapter.
We hope this helps.