signing an initramfs kernel

Embedded 1

On my i.mx8mp board I have secure boot enabled. I can boot a signed kernel fine. I'd like to now sign the kernel used with the initramfs image. I don't understand if that kernel is the same as the regular kernel and if I can just replace the signed kernel with it?

when I build my initramfs image recipe I get a few new files including a rootfs.cpio.gz file and a Image-initramfs file. I'm unclear what the differences are between these files.

If I unpack the cpio.gz file I see an Image file in /boot/Image. I don't seem to be able to boot this cpio.gz image though.