China has problems from its demographics, thats a long term decline they are trying to outrun by development of the country and things like AI perhaps will help replace the missing working population; losses of the 1 child policy over decades.
BYD is successful mostly but car companies generally seem to have problems with their profitability vs development, this is true in many countries. I'm more convinced of a wider story rather then just the 1 company as a problem
It is a large problem for a lot of car dealers all over the world.
More people want something affordable that works well. So high profit margin cars do not have the demand they once had.
Many just want a decent car that does not break and does not use a lot of fuel.