Problem with installation on FRITZ!Box 3390 (boot initramfs-kernel.bin is ok but check of the key linux_fs_start is not possible)

looks like this command is in a package that must be manually copied and installed.

Same procedure for 7412, but including details, how to enable that command:

where to get the ipk file (the version of package path and firmware file must match)
https://downloads.openwrt.org/releases/22.03.2/packages/mips_24kc/base/