In the event of a preemptive strike to counter foreign plans to initiate a special operation against China, soldiers on the ground must happen because it is by far the best way to deter and halt enemies coming in from the east direction by sea and air.
Having large concentrations of troops on the island means that even if China is attacked by an outsider, they must sufficiently degrade the PLA troops on Taiwan in order to even make landfall.
Once there are hundreds of thousands PLA on the island, they can rapidly remake cities on Taiwan into fortresses, they can also deploy anti ship missiles to prevent enemy amphibious assaults.
Only an air and naval presence is sufficient against the rebel army alone, but there is an inherent danger that a massive invasion force can breach the blockade and put down tens of thousands or even more troops on the island, turning the war into a potential stalemate.
Here the lesson from the current war is: would Russia have attacked if Ukraine had already occupied both Donetsk, Luhansk and had the ability to fortify them on the level of Mariupol and Bakhmut? Ukraine of course had neither air nor navy presence but especially not ground presence, therefore Russia was emboldened by their apparent weakness.
Sporadic Ukranian shelling of the rebels achieved no military results due to lack of firepower and accuracy. Another show of weakness.
Therefore as the situation on the eastern border deteriorates, China must not take things slowly, it needs to inflict a campaign of total annihilation against the rebel, thereby causing paralyzing fear into Korea and Japan who are close enough that similar campaigns can be done to them. Which means even if America wants to invade, they have no regional bases to support them, no rebels left alive to help them and where they wish to invade will be a fortress.