Basically, China pumps incredible amounts of money in to companies, so they can undercut prices from EU companies crazy - forcing the EU companies to give up. EU wants to level the playing field.
Edit: With taxes for Chinese companies that want to sell something in the EU, like China already does as well on the Chinese market.
There also another thing at play here: China has laws, so that foreign companies need at least 50% Chinese “shares” (it’s not just shares), basically neutering these companies and also giving away the technology to Chinese third parties. Wich further erodes the playing field, because now Chinese companies not only can produce stuff dirt cheap, they can also do it with “high-tech” stuff, without having to pay and/or do the development.