After upgrading u-boot, lts21 kernel works fine on raspberrypi 4B 1.4 4G DDR boards
Download WRL-LTS21 DISTRO "target-full-bcm-2xxx-rpi4.tar.bz2" $ sudo umount /dev/sdh $ cat wrlinux-image-full-bcm-2xxx-rpi4.ustart.img | sudo dd of=/dev/sdh bs=1M status=progress $ sync $ sudo eject /dev/sdh