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.