A page has been added to the SO3 wiki on how to debug SO3 and Apps on a Raspberry Pi 4 through JTAG (requires to be logged into gitlab).
https://gitlab.com/smartobject/so3/-/wikis/JTAG-Debug-on-Raspberry-Pi-4
This may come useful to debug bugs that appear only on the Raspberry Pi 4 and not in QEMU.