I'm going to slightly subvert the spirit of your question, because I think this is exactly what you referred to when you said "ruined by corporate interests", but Fedora Desktop would be my go-to Ubuntu replacement. Red Hat are very hands-off (I really don't think the analogy of it being a testbed for RHEL is accurate) and the stability is excellent. Additionally, SELinux is preconfigured, and flatpaks allow a very basic sandbox implementation via GUI (though it is far from perfect).
OTOH, if you don't give a shit about security (SELinux and AppArmor in particular) then try NixOS. Extremely powerful, idempotent system config. You can do Gnu Guix if you prefer but I have yet to be convinced by the Guix crowd it is superior, and since it has less apps I'm generally Nix-oriented.
OTOH, if you don't give a shit about security (SELinux and AppArmor in particular) then try NixOS. Extremely powerful, idempotent system config. You can do Gnu Guix if you prefer but I have yet to be convinced by the Guix crowd it is superior, and since it has less apps I'm generally Nix-oriented.