I have build the imx8mm for evk build root. The filesystem and dtbs are fine as long i flash the
rootfs.tar ontot p1 on SD or emmc,
Here are my out put files:
bl31.bin Image.gz imx8mm-spectra.dtb rootfs.ext2 rootfs.ext4 rootfs.tar u-boot.bin u-boot-spl.bi
I enabled u-boot which makes
./uboot-tools/imx-mkimage/iMX8M/flash.bin

Flashing that into empty space before P1 as
sudo dd if=./uboot-tools/imx-mkimage/iMX8M/flash.bin of=/dev/mmcblk0 bs=1024 seek=33
does not work.
I also tried to use the imx-mkimage as

for F in    "./buildroot-2022.11.2/output/images/bl31.bin"\
               "./buildroot-2022.11.2/output/images/imx8mm-spectra.dtb"\
               "./buildroot-2022.11.2/output/images/u-boot.bin"\
               "./buildroot-2022.11.2/output/build/uboot-2022.04/u-boot-nodtb.bin"\
               "./buildroot-2022.11.2/output/images/u-boot-spl.bin"\
               "./buildroot-2022.11.2/output/build/uboot-2022.04/lpddr4_pmu_train_2d_imem.bin"\
               "./buildroot-2022.11.2/output/build/uboot-2022.04/lpddr4_pmu_train_1d_dmem.bin"\
               "./buildroot-2022.11.2/output/build/uboot-2022.04/lpddr4_pmu_train_1d_imem.bin"\
               "./buildroot-2022.11.2/output/build/uboot-2022.04/lpddr4_pmu_train_2d_dmem.bin";do
       BN=$(basename ${F})
       echo "checking ${MK_FILES}${BN}"
       [[ -f ${MK_FILES}/${BN} ]] && rm ${MK_FILES}/${BN}
           cp ${F} ${MK_FILES}/
       ls -la ${MK_FILES}
   done
   pushd uboot-tools/imx-mkimage
      ln -s ../uboot-tools/imx-boot-tools/mkimage_uboot ./mkimage_uboot
      make clean
      make SOC=iMX8MM flash_evk
   popd

This came out clean as
./uboot-tools/imx-mkimage/iMX8M/flash.bin
Also flashing this flash.bin into does not boot at all.
Any ideas?
Thank you