Any actual guide on how to use ostree to make a DIY style immutable distro? - eviltoast

I don’t really understand how ostree works from a use standpoint. What I am looking to do is create a custom immutable Linux where I make a filesystem image and then devices can pull the image if I make changes upstream I’m looking for a way to update a local image.

So basically I’m wanting to create some sort of OStree repo. I know rpm-ostree exists but I want something that is more distro agnostic. (I want to use Debian and maybe gentoo as the base)