Is there any update on the support of the Matrix Voice on Buster (RPI4)?
I have the same problem with the creator.
After a lot of research it appears there is a breaking change in the Broadcom ALSA driver that is causing port audio to fail. It will not correctly select you default device.
The MATRIX Voice does work with the RPi 4 on Buster. However, our
matrixio-kernel-module package is currently down due to some updates which may be causing your problems.
A temporary solution is to purge the package installation of the MATRIX kernel modules and compile from source.
sudo apt purge matrixio-kernel-modules
Then, follow steps here.
Apologies for any inconvenience and please reach out if with any further questions/concerns/suggestions.