it's actually "kuai" (pronounced same way as popular incorrect name of famous The Bridge on the River Kwai (the correct name is K(h)waE)) in Chinese streets, if you use yuan or renmimbi you will sound like you pretend to be some snobbish TV news host

I don't think I've ever used anywhere in street, shop or restaurant yuan/renmimbi, at least not in Beijing and around, some people may use yuan, hardly anyone renmimbi

here you have AI answer based on Reddit thread, which I can confirm is correct:

"In everyday spoken Chinese, kuai (块) is overwhelmingly the most common term used to state prices. Yuan (元) is used in formal writing and official contexts, while renminbi (人民币) names the overall currency system like "Sterling" or "USD" rather than a daily price unit."