At this point, legal to disseminate. I won’t say this with absolute certainty but with reasonable certainty that the people/governments that have the technology, scientists, and finances to build an atomic weapon could if they wanted to because the information is available for the right price. But it’s complex, expensive, and unless you’re very good at hiding your endeavor, others at your level are going to notice where the rare and important minerals for enriching uranium are going. You can’t just dig up a rock containing uranium and build a bomb, but they’d notice if you suddenly took an interest in acquiring rocks that could be enriched, as well as notice if you were trying to get your hands on enriched uranium (or whichever rare source material you intended on using). I would doubt even the most structured, financed, and well organized terrorists, cartels, or warlords could build one even if they had detailed instructions, and no one’s building one in their basement in their spare time. Dirty bombs or someone getting their hands on a black market nuke (both very unlikely) would be something I would be more concerned about than someone building a nuke from scratch.

I’ll end on one example. The submarine billionaire who imploded himself. Schematics for deep sea subs exist, he had access to the kind of money that could have built one. He tried, he died. Now imagine that with nukes. Dude would have irradiated himself to death before he even started assembling it.