I see many videos on youtube where they tell you to get residency visa in countries that are unlikely to be involved in a world war 3.
Is it really enough to have a residency visa? I think the country you are a citizen in can still force you to come back to join the war if they want to. Either they already have such a law or they can create one when it's time. The country you would have a residency visa at would have to deport you. I think the only way to avoid such a situation is by getting citizenship in a country that is unlikely to join a war, so residency is not enough.
And it might not even be enough with dual citizenship. Because the origin country could change the law and forbid dual citizenship and then the country you got a dual citizenship at would have to remove your citizenship and deport you. So you would have to renounce your citizenship with the country you think is likely to join a war.
Getting a resident visa to a new country where you plan to live on isn't that easy. If you have no money, you'll have to go through with years of working and living there. While there are golden ticket visas that are a shortcut process to your resident visa and passport and that's through investing or buying it to those countries. Many countries offer this and I think many are choosing those countries in the Carribbean part because it's easy to get a passport there and you can live there if you have money. Most likely it's ranging from $100k and more than $250k.
There are many countries that grant asylum visas to citizens of countries considered unsafe, such as Syria before the fall of the Assad regime and Afghanistan today. If World War III breaks out, the countries involved in the conflict will certainly no longer be considered safe, and citizens will be entitled to seek asylum in safe countries. These safe countries may not be able to provide significant support. For example, if I were granted asylum in Switzerland, the government would provide me with a salary until I could find a job, but compared to other countries, I might not be able to receive anything.