See ongoing discussion thread, but the tl;dr is that attempting to run both Outer Rim and Nexus Extended Endgame causes an error on load, regarding missing science packs. The current version of the error with Outer Rim v0.3.3 and Nexus Extended Endgame v1.0.0:

Failed to load mods: Technology antimatter-containment-fields-generator: there is no lab that will accept all of the science packs this technology requires.

Science packs: automation-science-pack, logistic-science-pack, military-science-pack, chemical-science-pack, production-science-pack, utility-science-pack, space-science-pack, cryogenic-science-pack, metallurgic-science-pack, agricultural-science-pack, electromagnetic-science-pack, promethium-882-science-pack, antimatter-science-pack

After doing some debugging from the Nexus Extended side, when it completes its data-final-fixes, the antimatter-containment-fields-generator requires Cryogenic Science Pack, but for some reason, that is not allowed in the Omega Lab (which may or may not be the only lab that accepts promethium science? Didn't test that far). When the Outer Rim mod is disabled, Nexus Extended's Omega Lab does have access to the Cryogenic Pack at the end of its data-final-fixes

I'm not sure which side the error lies on, but the Nexus dev tried to fix with the release v1.0.0, but that doesn't appear to have worked as of Factorio stable v2.0.69

What is the current state on this?
I saw some of the discussion on discord but not reading these threads as often as I probably should.

Oh, funnily enough, it's the exact opposite for me; I haven't been checking the Discord very often lol. I have email notifications on for discussion threads and check them every day, so I see these much more often.

Anyways, looks like you already figured out what the cause was, from the Nexus Extended side of things?