Poor nations can benefit from Bitcoin if they invest in it. Countries like El Salvador and Bhutan have invested massively in Bitcoin and I guess that they are now in profit.
AFAIK they have not sold their bitcoins which means you can't really say they've made enough profit to solve their problems. They just have an asset in their reserves that has appreciated in value and economic problems won't be solved just by having a valuable asset "in the vaults".
You are right, El Salvador is yet to sell but the Royal Government of Bhutan has sold about $33.5B of its Bitcoin late last year. However, the country still holds close to 12,206 Bitcoins as of last year.
https://coinmarketcap.com/academy/article/bhutan-cashes-out-dollar335b-in-bitcoin-still-holds-dollar111b-in-btc