Strategypage notes China's military-compatible civilian shipping:
In May 2015 China was seen using a 20,000 ton civilian RO/RO (Roll On/Roll Off) ferry for transporting troops and vehicles during an amphibious training exercise. This was no surprise because since 2000 China has offered subsidies to shipping companies to make a few modifications to ferries and other RO/RO ships and agree to make them available to the military for amphibious training and during wartime. For decades China has used a system where it keeps track of hundreds of commercial ferries and barges that can be mobilized by the military and used for amphibious operations against Taiwan. It is believed that there is sufficient lift for about a dozen divisions plus non-specialized ships (mostly civilian) for moving support units.
A dozen divisions is quite a bit. Add in three parachute divisions and an airmobile "urban light cavalry" division, and Taiwan will have serious problems if the Chinese manage to get ashore.
And remember that's initial lift of troops. Those ships can go back to China to load more for the second wave.
I recently noted new Chinese regulations on building civilian ships so they can more easily be adapted to military use.
The dedicated amphibious warfare ships are good for capturing small islands in the strait and the South China Sea (or East China Sea).
But the civilian ships would be vital to assault Taiwan.
Put aside your dismissal of China's ability to invade Taiwan. They might fail. But they have the capability to try.
UPDATE: And they are building up their visible formal assets, too.