They don’t need any additional motivation at this point, generations of mainland Chinese have been brainwashed into believing that Taiwan is their land, despite that not being the case for centuries.

All they need is an opportunity to open up, where western militaries are occupied elsewhere, such as Europe after a Russian attack on NATO, the US gets pulled in to the Middle East again or the South American war crimes that Trump is doing becomes a much larger war. As soon as they think nobody will come to Taiwan’s aid they will invade.