Universal Blue (Bluefin etc.) has a reusable GitHub template. https://github.com/ublue-os/image-template
... and it works fabulously. I have been running Bluefin (same folks as Bazzite) from one of these templates for about 6 months and it has been a near on flawless experience. I have moved from Fedora 40->41->42 without having to touch a traditional "upgrade".