Don't like posting a long comment, but re-posting a high-level chronological view of the problems past 15 years:
1) forced technology transfer/IP theft -- all foreign automakers/EV battery producers forced to give up IP to access China's market (and subsidies). This was litigated before the WTO by the EU in 2018 (see WT/DS549):
Hybrid in a Trade Squeeze, Keith Bradsher, Sept 5, 2011, NYT
... The Chinese government is refusing to let the Volt qualify for subsidies totaling up to $19,300 a car unless G.M. agrees to transfer the engineering secrets for one of the Volt’s three main technologies to a joint venture in China with a Chinese automaker, G.M. officials said.
2) Once foreign battery producers made IPR/IP concessions to access China's growing EV market and significant investment in battery production in China, they were effectively banned. All domestic, foreign automakers were likewise forced to switch to local champions, namely CATL/BYD, promoted under MIIT's 2015 "Regulation on the Standards of the Automotive Power Battery Industry”:
Power Play, Trefor Moss, May 17, 2018, WSJ
... 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.”
3) Picking winners and losers: made sure no Chinese consumers had access to EVs with batteries from foreign EV battery producers effectively creating a captive market of buyers for CATL/BYD.
Why a Chinese Company Dominates Electric Car Batteries. Keith Bradsher and Michael Forsythe, Dec 22, 2021, NYT
The government soon said electric car buyers could get subsidies only if the battery was made by a Chinese company. G.M., which had not been notified of the rule, started shipping Buick Velite electric cars in 2016 with batteries made in China by LG, a South Korean company.
Angry consumers and dealers complained that local officials were denying them subsidies, people familiar with the episode said. G.M. switched heavily to CATL for the huge Chinese market.
4) another fairly recent example of China's arbitrary regulatory barriers to keep out foreign competition, which was later dropped after the gov't found out their local "champion," CATL, couldn't pass the EV battery safety test:
Why a Chinese Company Dominates Electric Car Batteries. Keith Bradsher and Michael Forsythe, Dec 22, 2021, NYT
... A rival had released a video suggesting that a technology used by the company, CATL, and other manufacturers could cause car fires. Imitating a Chinese government safety test, the rival had driven a nail through a battery cell, one of many in a typical electric car battery. The cell exploded in a fireball.
Chinese officials took swift action — by dropping the nail test, according to documents reviewed by The New York Times. The new regulation, released two months later, listed who had drafted it: First on the list, ahead of the government’s own vehicle testing agency, was CATL.
Then, you also have China weaponizing their EV raw-material supply-chain, such as EV-grade graphite used as battery's anode material. China torpedo'ed Swedish battery company, Northvolt, with an export ban in 2020 because Sweden protected Chinese dissidents and called out human rights violation. Northvolt went bankrupt last year.
re: subsidies. China's consumer direct purchase subsidy ended in Dec 2022, but was extended again as tax credit for another 4 years in Jun 2023. Just to be sure though, there are many other subsidies besides the consumer subsidies at every layer of China's EV/battery supply-chain. The EU's anti-subsidy probe last year (see Regulation 2024/1866) for instance evolved around "export subsidies."