Well, it is not!
The audio was playing, however, at a terrible quality, not worth further talking about.
While the RPi400 was never meant to be used in my amateur radio setting, it now shows clearly to not be suitable for such use at all. The only thing still untested would be SDR devices such as the SDR-Play RSP1A.
Seen that a simple audio dongle does not work well, I have serious doubts about any of the SDRs being better supported,
If the Raspberry Pi Foundation is reading, please consider adding an AV jack to a future version of the RPi400. The form-factor of the device is excellent, having it performing similar to a RPi3B+ in respect to audio would make this device usable for not just the ham radio community but also so many more folks looking for some audio abilities of a device.
