China would never be able to take Tawain even without help from the US. The PLN has a lot if ships, but they are small - so making a beach landing would be an extreme challenge.

The west coast of Taiwan has been reinforced against such an invasion over the past 50 years, so China would have to sail around and attempt a landing on the east coast. Now, that wobt be a leasurely cruise has Tawain as hundreds, if not thousands of surface to ship missiles. So the the PLN would have to deal with that in addition to the Tawainese Navy.

China also doesnt have the airlift capacity to insert a meaningful force and Tawain does have a legitimate Air Force as they are rocking the latest F16 vipers.

Once past these obstackes, the PLA force that lands would have to face off against an entrenched Tawainese Army, 150,000 strong and equiped with the latest US Hardware.

Now let us consider the fact China has only one Ally, North Korea. Now let us consider that the US has multiple; Japan, South Korea, Singapore, Australia, New Zealand, etc.

Furthermore, the US President is required by law to come to the aid of Tawain - and when the US gets involved, they bring all the boys.

The most China could hope to do is rain down cruise missiles on Tawain, but that wouldnt achieve any real military goals other than killing 1000s of civilians.