Nuclear weapons are horrendously complex, and require exotic, difficult to refine materials. I'm not surprised a lone nut hasn't been able to build one.
Now CRISPR derived viruses that make Covid look like the hiccups? That someone could probably do out of their garage. Kits are available online!
You couldn't engineer a custom virus in your garage. You absolutely could weaponize anthrax or produce an organophosphate nerve agent though with a pretty low bar of effort.