The problem is you need to bring the ground force from China to Taiwan. And Individual PLA soldier can't fly to Taiwan and fight a ground war, you need to insert the Unit to Taiwan somehow, and that very much depending on How big of an Army you can transport and how big of an army you can support.
Indeed China have 2 millions strong PLA Ground Force, but that does not translate to all 2 Millions would send to capture Taiwan.
A.) How much your troop ship and transport plane can carry each load.
Don't take PLA as an example, take US Military as an Example, which is currently the greatest Army on the account of Sealift and Airlift Capability. US Military which have 300 Naval ship of all type which can transport about 200,000 Soldier each single trip and USAF current have about 500 Large Troop Carrier (222 C-17, 265 C-130H, 89 C-130J) which can take anywhere between 40,000 to 45,000 Troop.
List of Military Sealift Command ships - Wikipedia, the free encyclopedia
List of active United States military aircraft - Wikipedia, the free encyclopedia
Now, Even if PLA reaches this level of Lifting Ability (Which currently less than 1/10 to the US Sea and Air Lift Command), that mean for the first 5 hours (A round trip from China to Taiwan by sea), the Chinese can only land about 250,000 to Attack and Secure any objective. Which the first wave would face the full force of ROC Military, which currently have 300,000 active and 2 million reserve personnel. And that's if PLA can land and drop all its forces without any challenge, loses will happen to the first wave, either by sinking the Naval Transport by Submarine or Surface Ship or Downing of Air Transport with SAM or Fighters.
Then You can put a little less troop to the shore the second wave, then the third wave, then the fourth wave.
B.) Beside sending in force, you also have to consider the way to supply your force, meaning part of your sea/air lift power will be diverted to support the troops on ground by transporting food, ammunition, replacement parts, daily necessities, instead of carrying troop. You can keep sending in people to shore and when they finish what they brought with them, how do you supposes to carry the fight on when the 300 or so round you brought with expanded in the first hours??
C.) Beside Troop transport and Supply you also need to consider leaving a considerable force behind to Guard/Reserve
It's not about How PLA could and would take, but how can you justifies losing a great deal and quantity of men and equipment to recover a rouge province?? China is technologically advance than Taiwan, but still, they are not far behind, unlike Iraq and US, even so, the Coalition suffer 150,000 Casualty (included 25000 killed) you can imagine if China invade Taiwan, a near peer in an fortified Island position, you are talking about Casualty in Millions and that is BEFORE US Involvement