This is a big deal because China has tricked one of its trading partners into accepting their magic beans for a significant amount of oil. There is almost certainly a good reason why the other party doesn't want to be named. They are only willing to accept this deal because they are under significant international scrutiny.
Here's the problem with trading with a currency that isn't USD. When Russian invaded Ukraine and came under U.S. sanctions, India offered to exchange Russian oil for rupees. Russia thought that was a good idea, and so they proceeded to sell Russian oil (at a discount) to India for rupees. Fast forward to today and Russia currently has a balance of nearly $200 billion worth of India rupees that it can't spend (that's a lot of rupees). India traded those rupees for oil, but now it won't let Russia trade those rupees for anything but Indian goods and services (and not at market prices at that). Russia doesn't want that much overpriced Indian goods and services, so it has stopped accepting rupees for trades for oil. In many ways what India has done to Russia is worse than what the U.S. did to Russia. The U.S. merely said that they were unwilling to trade with Russia (or allow other countries to trade with Russia using its banking system and currency). India, in a far shrewder move, stole hundreds of billions of dollars worth of Russian oil.
Well played India.
That's basically the reason that the rupee is unlikely to ever become a significant reserve currency, despite the fact that the BRICs nations all wish that they could use something besides the dollar. India is not willing to give up the control over rupee prices that is required of a reserve currency. No one wants to be like Russia and find out, after the fact, that they have $200 billion dollars worth of rupees that they can't sell. Russia has since switched to doing oil transactions in Chinese yuan, even with India. This is better for Russia, as China makes lots of stuff that everyone wants. However, there are significant problems with using the yuan as a reserve currency as well. The primary issue being the severe transaction controls that China puts on the yuan. China does not want a strong yuan as that would make their exports less competitive around the world. There's a reason that so little of the world's transactions happen in yuan, and it is because China is not willing to open up their economy to the extent that would be required.
China's e-CNY is even worse than the rupee or the yuan as a reserve currency. This is primarily because it is not actual yuan, but is rather a separate, even more highly controlled, digital token. Even it's most anonymous accounts require a cell phone number to be tied to the account, and all accounts have very low balance caps, daily transfer caps, etc. You can get business accounts, but they require even more onerous terms. You definitely can not move money out of e-CNY without permission from the government, and even if you want to purchase stuff with e-CNY you will find yourself paying a premium for this very unpopular way of transacting business.
These tokens are, apparently, being used to make transfers between banks, but for those transactions I suspect that the government has allowed the banks ot simply use them as like a stablecoin, meaning it is easy to simply pretend they are yuan. In short, it would probably be easier for everyone involved if they left e-CNY out of the equation entirely. These transactions are not actually the market, they are just there to show that some volume is happening.
Think of it as if you had stablecoin tokens on Binance in the U.S. You used to be able to just withdraw those as dollars from your bank. Now, however, if you want to purchase something in dollars, you have to find another institution that is willing to trade your stablecoin for actual dollars and then withdraw those dollars. That's still possible today, for the sorts of amounts that most cryptobros are likely to withdraw, but what would happen if you needed to move $1 billion dollars. You probably get told that the max withdrawal is $10,000/day.
e-CNY is like that, except there are no third-party exchanges where you can exchange e-CNY for anything. China is happy to give you e-CNY for your goods, but good luck turning e-CNY into something that you actually want, especially at scale.
Whatever is happening though, it is nonsense to think that this represents some sort of shift towards a new reserve currency. Like India buying oil with rupees from Russia this is mostly just China taking advantage of some country that doesn't have access to the actual global market. The Western world has decreed that whoever it is can't do business in dollars (or euro), and so they are forced to take a deal that is possibly a step up from India buying oil with rupees that it won't let Russia spend. Whoever is accepting e-CNY it is super likely that they are getting absolutely raped. They are only doing this transaction because they have no other choice. The second the embargo disappears whoever this is will go back to requiring dollars for their oil. In the meantime China is taking advantage of the situation to purchase oil at a ridiculously low price.