Hi there,
I’d like to share my setup with the community and ask for advise to get this up and running.
I am using an Oratek Tofu Board mit a Wester Digital SN520 2230 NVME SSD and a CM4 with eMMC storage.
My Zigbee HAT is the CC2652P2 PI Module.
Flashing the OS with the RPI Imager works fine for the eMMC & NVME and I can boot from either NVME or eMMC, depending on the boot order config. The build quality of the board is amazing. So far so good, but I also want to use SSH and get my Zigbee HAT working … 
Where I am stuck:
I want to import SSH keys with a USB stick and get the Zigbee HAT working.
I know that I have to edit the /boot/config.txt (enable USB, disable BT), however I cannot access/find the config.txt when the HA installation is either on the eMMC or on an NVME. I did connect the NVME with a USB adapter to my Mac and also used the mass storage gadget for RPIBoot to access the NVME - no luck and I cannot access the /boot partition. I used a Ubuntu VM and tried to mount the NVME partitions - no luck.
Where does the /boot/ partition sit? I assume on the drive where the HA installation/image is flashed to. Am I right?
Any advise how I can get this working?
Thanks much!