Upgrade from Jetpack 4.6.1 to dev preview 5

I can’t answer, but is it correct that your NX is a dev kit (using SD card)? If so, then boot content is on the QSPI memory, which is part of the board itself, and not on the SD card/rootfs. You would have to flash the Jetson itself with JetPack/SDK Manager to get the correct boot content. However, I don’t know if the DP 5 supports the NX dev kit or not.