As I said, in the process of creating my own. The secureblue creator and "boss" has permabanned me for asking "critical" questions. Its all transparent on the internet, the things he used as reasons are hillarious. (I just never saw a reason to make that gossip public, also my contributions were not that many).

But the secureblue project is really good in many parts, I agree with many things, just not with some that are poorly pretty dealbreaking.

For example: Fedora has RPM firefox in their base image, uBlues base images keep it, secureblue removes it. Rpm-ostree is confused and adding it back is not possible. Yay!

So there are 2 options:

The better one: use blue-build and secureblue as base image, revert some opinionated changes (like uninstalling RPM Firefox which is simply the best browser on Fedora. Librewolf is made for f38, Flatpaks are not complete and probably insecure, Chromium sucks (I tried to use it) and crashes all the time (on secureblue)).
The annoying one: hard fork it (if you are blocked you are not allowed to fork a project, making this even more annoying). Change the things and constantly keep track of secureblue, which now has a few people working on it.

So yeah it is a pain. I am experimenting with both, lets see.