Thank you @KevinFFF for your prompt reply.
boot/boot/dir is on production board with encrypted root_fs;
I’m flashing devkit at the moment to check the differences.
My modifications were focused only to enabling LUKS encrypted partition:
At the moment, I just want to understand if it is typical to have boot\boot structure for APP_ENC mounted to root anb APP mounted to /boot
Custom IMX477 drivers are separate complicated topic, Arducam deb package trying to mount /mnt/APP because detected that not APP mounted as root (some automation for NFS case) It seems wrong operation for my case and we are trying to prevent it with @naxty