It's not just mere "subsidies," there is also blatant protectionism. CEOs of incumbents car makers have been warning against the Chinese gov't unsavory anti-market practices to protect their local battery companies and achieve market dominance past 10 years, such as:
1. Power Play: How China-Owned Volvo Avoids Beijing’s Battery Rules Car maker is allowed to use high-end foreign technology, while rivals are squeezed into buying local, Trefor Moss, May 17, 2018, the Wall Street Journal
... China requires auto makers to use batteries from one of its approved suppliers if they want to be cleared to mass-produce electric cars and plug-in hybrids and to qualify for subsidies. These suppliers are all Chinese, so such global leaders as South Korea’s LG Chem Ltd and Japan’s Panasonic Corp. are excluded.
... Foreign batteries aren’t officially banned in China, but auto executives say that since 2016 they have been warned by government officials that they must use Chinese batteries in their China-built cars, or face repercussions. That has forced them to spend millions of dollars to redesign cars to work with inferior Chinese batteries, they say.
... “We want to comply, and we have to comply,” said one executive with a foreign car maker. “There’s no other option.”
2.
Why a Chinese Company Dominates Electric Car Batteries, Beijing gave CATL lavish subsidies, a captive market of buyers and soft regulatory treatment, helping it to control a crucial technology of the future. Keith Bradsher and Michael Forsythe, Dec. 22, 2021, The NYTimes
3. The Key to Electric Cars Is Batteries. One Chinese Firm Dominates the Industry. Beijing built the world’s largest EV market, then pressured foreign car makers to use its batteries, Trefor Moss, Nov. 3, 2019, WSJ
... China is by far the biggest EV market, and to boost its standing in the fast-growing industry, China began pressuring foreign auto makers to use locally-made batteries
... Auto makers weren’t pleased, but they fell in line. During a visit to CATL headquarters in 2017, three Daimler AG executives displayed their irritation shortly after the meeting started, recalled Jiang Lingfeng, then a CATL project manager who prepared a technical briefing for the visitors. One Daimler executive cut off his briefing, said Mr. Jiang. “We’re not interested,” the executive said, according to Mr. Jiang. “The only reason we’re here is that we have no choice, so let’s just talk about the price.”
... Still, auto makers bridled at CATL’s dominance, according to Mr. Tsao, the former supply-chain manager there. CATL’s batteries also cost 25% more than those of leading rivals because the company was still learning to mass-produce cost-effectively, he said. “The price is high, and the service is slow,” he said, summing up CATL’s proposition to auto maker clients.
... “What the government did was a good thing for China,” said Mr. Jiang, the former CATL project manager. “Without its restrictions, I don’t think CATL would ever have been successful.”
Let's not forget that the EU also followed up with a WTO complaint against China for their NEV regulation that forced tech transfer (see WT/DS549) in 2018, and waited over 6 years to take a countervailing measure (2024/1866) against prohibited subsidies practices.