Just a note on why flashing with SDKM is required. The boot is rejected very early on. Regardless of whether or not this is an SD card model there is memory on the Nano itself (part of eMMC if eMMC model, part of QSPI memory if SD card model) which flash installs, and which must be a version consistent with what the rootfs partition has. Do note that some of this content is signed, and even if using the default of a null signing (a NULL key is still a key and is the default when flashing without specifically setting keys), it must be signed correctly. Flashing should set up all of that early boot content for you. Then the boot log should go much further. There is a minor variation of this in both logs.