A country is big and complicated with many elements that decide its success or failure, and Bitcoin as a single element, can not change a failed nation to a succesful one. It's unrealistic mission for Bitcoin and Bitcoin does not have that mission when it was created by Satoshi Nakamoto.
It's clickbait trick by politicians or Youtubers or people who want to make noise on social media.
It can only save a country economically - El Salvador is a good example of this. Argentina (to a limited extent) too.
If the country has other kinds of problems that are not financial in nature then Bitcoin is going to do little to solve those. For example, take these 'immigration crisis' or 'gang violence' problems that many countries have. Obviously, Bitcoin is not going to help there at all.