main VS isogenerator

Best place to start is to get rid of all the layered packages (RPMFusion) on top of the immutable image then swap to the ublue-Nvidia images that have all the codecs and Nvidia drivers built into the image itself.

If you're using Nvidia I'd recommend using Fedora Kinoite with the ublue-Nvidia image that comes with the Nvidia drivers pre-built in. That eliminates a big chunk of issues with their drivers which is just building the damn things. AMD and Intel drivers are built into the kernel and require zero effort.

What you are looking for is UBlue, https://github.com/ublue-os/main.

It's a variant of Silverblue with Nvidia drivers built in.

If you're using Nvidia, then install using the ublue Nvidia image which has the drivers built in, cause they can be a prick to manage otherwise.

What these sort of introductions to immutable always fail to consider is the other side of the coin, image-based. I'm working on https://universal-blue.org/ along with many people much more skilled than me. We build OCI container images on top of vanilla Fedora Silverblue & many other editions with different desktops. Those images can then be booted to (or rather rebased to) using rpm-ostree. This is a more robust way of extending the system than layering, and the same changes can be easily benefited or inherited from by anyone. You can even make your own image really easily!

I think that VanillaOS and SUSE are working on similar things, but we're not an OS project, just a downstream from Fedora. Fedora's full support is underway but with what's already working perfectly our methods are already IME some of the most robust and easy ways of delivering Nvidia drivers for example.

Download: https://github.com/ublue-os/main/releases/tag/v1.1.8

For the isobuilder, I would really suggest that you use the long-form Lorax builder above (the templates are in their repo) rather than mkksiso. This seems like added complexity for no reason, but outside of sucking bandwidth that you're paying for every time someone fetches it from cloudfront, the way it's currently done more or else forces anyone who downloads the ISO to re-fetch the compose, and use more bandwidth, or just outright fail in airgapped environment, and it's sure to make your CI (if you have CI around the ISO) much slower than it needs to besides.