Excluding Fedora because it’s “too close to RH” doesn’t make any sense at all. Fedora is not controlled by Red Hat, and Red Hat has no interest in a consumer desktop platform that they can’t sell. Fedora’s development is managed by FESCo, a community elected board that represents the interests of the community. They are kept intentionally separate from Red Hat’s development, and don’t tailor their development to Red Hat’s wants or needs (in fact they often do the opposite, as Fedora pushes for change in the way things are done, not stability, as can be seen by the exclusion of X11 from Fedora 40, for example). That stands in direct contradiction with RHEL’s goals. The features that are pushed by Red Hat developers would not be approved if they stood against the wants of the community, so anything Red Hat does contribute benefits the community as well. Red Hat’s entire business is in enterprise solutions, as their business model relies on them selling support for their software. There is exactly $0 in potential revenue from Red Hat trying to take over Fedora, it just doesn’t make sense. They can’t sell anything, and since Red Hat doesn’t employ all of the thousands of active contributors, such a takeover would simply result in a new fork. In fact, it would be against their interests, as Red Hat actively benefits from the developments of the community. Taking over control of the project would lose them all of the constant volunteer work put in by the community, which costs far less for them to sponsor than it would to employ a team a fraction of the size on salary. I’ve discussed this topic at length many times before, so I’ll just link to a few comments that explain the situation in more detail (including how the project is funded, managed, and separated from Red Hat).
The best fit for your criteria is Fedora. If you want uBlue spins, you’re still getting Fedora, just a more opinionated version. All of the major development of uBlue’s images comes from Fedora though, as they don’t maintain their own distro, they just repackage Fedora.