Just to put an invasion of Taiwan in context, the following is an overview of resources required for the D-Day landings:
On D-Day, the Allies landed around 156,000 troops in Normandy. The American forces landed numbered 73,000: 23,250 on Utah Beach, 34,250 on Omaha Beach, and 15,500 airborne troops. In the British and Canadian sector, 83,115 troops were landed (61,715 of them British): 24,970 on Gold Beach, 21,400 on Juno Beach, 28,845 on Sword Beach, and 7900 airborne troops.
11,590 aircraft were available to support the landings. On D-Day, Allied aircraft flew 14,674 sorties, and 127 were lost.
In the airborne landings on both flanks of the beaches, 2395 aircraft and 867 gliders of the RAF and USAAF were used on D-Day.
Operation Neptune involved huge naval forces, including 6939 vessels: 1213 naval combat ships, 4126 landing ships and landing craft, 736 ancillary craft and 864 merchant vessels. Some 195,700 personnel were assigned to Operation Neptune: 52,889 US, 112,824 British, and 4988 from other Allied countries.By the end of 11 June (D + 5), 326,547 troops, 54,186 vehicles and 104,428 tons of supplies had been landed on the beaches.
Just look at the shear numbers of assets required to mount a successful landing, and this was against an occupying army (weakened through years of conflict on the Eastern front), not a indigenous armed forces supported by a local population.
The PRC does not own enough assets to lift the man-power from Xiamen to Taiwan required to subdue and hold the island. Plus only 15% of their huge standing army could be considered a modern, well equipped and trained offensive force. They also have zero experience at such complex operations. Other than a protracted bombardment campaign supported by a fifth-column targeting key politicians and military leaders they have very little alternative option.