Why wouldn't Iran accept Yuan? Without doing anything special, China is becoming the most reliable trade partner in the world.
This tactic, used against Russia, Iran, and others, has turned them to seeking other, safer currencies. The Euro is risky; EU members are American allies, generally speaking, and also may act against Iran, etc. for their own reasons. The most widely used currency and most stable economy (an unstable economy causes and unstable currency) is the Chinese yuan or renminbi.
If you sell something for $10 billion US dollars then you can use that money to buy almost anything in the world. If you sell it for equivalent yuan, your options are much more limited. For some things you might need, it could be similar to showing up to a shopping mall in Chicago with yuan - you effectively have no money (without finding a way to convert them to dollars, which brings you back to the original problem).
Also, while China is a major economic power, they are not considered as stable as the US government (though the gap is closing quickly). Your $10 billion in yuan today might be worth $9 billion tomorrow.
Just by doing this, Kenya saved 215 millions USD... on a Chinese USD loan. [2]
1: https://www.chathamhouse.org/2026/01/chinas-12-trillion-trad...
2 : https://www.bloomberg.com/news/articles/2025-10-07/kenya-sna...