Thank you for putting this together - I have been struggling to get it working!!!!
I noticed that you are using HTTP to send/receive data between the MPU and MCU I have been trying to use it direct without using HTTP - wonder if that is even possible?
That was created by @facchinm in response to one of the issues/prs on SPI3 - when I find the link I will post it.
EDIT: here is the link I mentioned: unoq: enable spi peripheral interface by facchinm · Pull Request #383 · arduino/ArduinoCore-zephyr
and to the original discussion on getting SPI3 test case working:
How to install python packages on the Arduino Q - UNO Family / UNO Q - Arduino Forum