It’s not an issue of nfed nor ncs, but Zephyr itself:
Using mcuboot for nRF91 without SECURE_BOOT is broken. That currently breaks all update paths using that option.
If using the external flash as upload partition works, is not known by me, I don’t use it.
See Zephyr - issue 117802
and DevZone - NCS 3.4.0, nRF91, DFU without external flash and without SECURE_BOOT is broken
