Thanks for confirming /boot/extlinux/extlinux.conf is no longer needed.
I have deleted from the rootfs and now flash.sh with JP5.0 fails with
...
[ 0.0301 ] Assuming zero filled SBK key : not reading
[ 0.0330 ] tegrahost_v2 --chip 0x19 0 --updatesigheader 1_kernel_tegra194-p2888-0001-p2822-0000_aligned_sigheader.dtb.encrypt 1_kernel_tegra194-p2888-0001-p2822-0000_aligned_sigheader.dtb.hash zerosbk
[ 0.0371 ]
[ 0.0377 ] Signed file: /home/koi/workspace/xavier_34.1.0/Linux_for_Tegra/bootloader/temp_user_dir/kernel_tegra194-p2888-0001-p2822-0000_sigheader.dtb.encrypt
l4t_sign_image.sh: Generate header for kernel_tegra194-p2888-0001-p2822-0000_sigheader.dtb.encrypt
l4t_sign_image.sh: chip 0x19: add 0x5c9f4 to offset 0x8 in sig file
l4t_sign_image.sh: Generate 16-byte-size-aligned base file for kernel_tegra194-p2888-0001-p2822-0000_sigheader.dtb.encrypt
l4t_sign_image.sh: the signed file is /home/koi/workspace/xavier_34.1.0/Linux_for_Tegra/bootloader/temp_user_dir/kernel_tegra194-p2888-0001-p2822-0000_sigheader.dtb.encrypt
populating kernel to rootfs... done.
populating initrd to rootfs... done.
populating kernel_tegra194-p2888-0001-p2822-0000.dtb to rootfs... done.
Making system.img...
/home/koi/workspace/xavier_34.1.0/Linux_for_Tegra/rootfs/boot/extlinux/extlinux.conf is not found, exiting...
It didn’t even get to the hang stage that I mentioned in the other thread.