Upwork allows freelancers from over 200 countries.
Upwork has NOT selected specific countries that it won't allow users from.
There are a small handful of about 5 countries that Upwork can't allow users from - not by any choice of its own - but because it is following U.S. trade sanctions.
And those countries weren't randomly selected. Those countries are on a trade sanction list because of things that those countries do. So this has nothing to do with the original poster, or Upwork, or even the U.S.
The reason the original poster can't work on Upwork is due to the things his country's government does. Sanctions have been in place since 1979. When his country's government stops doing those things, then the sanctions will be lifted and Upwork will allow users from that country.