I have flashed my jetson nano with secure boot enabled and fuse burned. Can I flash it with Yocto image?
Unless this is an eMMC model you won’t be able to enable secure boot (this requires burning fuses, and in turn, this requires eMMC). I’m assuming this is an eMMC module on a third party carrier board (although you could have put this on a dev kit carrier board). So long as you have the keys there is no reason you cannot put Yocto on. The real issue is usually that the boot chain likely needs to be adapted for the Yocto rootfs (this gets easier in L4T R36.x, but that isn’t available on older Nano; requires Orin or newer).
Assuming you do have security fuses burned, then keep in mind that the kernel, device tree, and other parts of boot can no only be referenced from the signed eMMC binary partitions. Certain options in the extlinux.conf file are no longer honored (secure boot wouldn’t be very good if you could substitute kernel or device tree just from an edit to extlinux.conf). Once fuses are burned you would have to use flash to change the kernel or device tree.