Most countries definitely do not have nukes. There are a handful that could have them in secret, or that maintain the materials to make them immediately if needed. But all of those combined would amount to no more than a few dozen, small, nuclear weapons. There are not a thousand Tsar Bomba size nukes secreted away.

If the US and Russia stood down and the rest of the world let loose all of their nukes, it would be insufficient to cause sufficient damage to the technological integrity of our species such that backyard solar manufacture becomes viable.