The only issue right now about China and magnets is that China has a world dominating position in possessing and processing the rare earth minerals
Remember they aren't rare.
China tried this once before - in the late noughties. Limiting exports to force the price up. However because they are new to capitalism, they failed to realise that this would make previously unviable non-Chinese sources of rare-earth minerals, viable. Which is exactly what happened. (A similar thing happened with tin, which led to Cornish tin mining being a thing again).
However the Chinese (unlike the west) learns form it's mistakes. They are not going to be blindsided again.