I don't think PLA has ever been soft to their opponents during fire fights, they usually give all they have thrown at their enemy, the huge number of KMT deaths can be testimonial to this. However, after the battle is over, PLA can be soft to their prisoners, as shown by their treatments of war prisoners (KMT soldiers in civil war, imperial Japanese in WW2, Korean war UN soldiers and Indian soldiers in China-India border war/conflicts).
In any fire fights against ROC soldiers in Taiwan, PLA is not expected to fight like Russians in Ukraine. An enemy is an enemy, there won't be any mercy unless they surrender. Civilians will be given the opportunity to leave battle zones before fire fights and during ceasefire, and those that decided to stay will have to take their chances.
Classic PLA war doctrines is to fight the enemy outside cities, then sorround the city and negotiate with the defenders inside to surrender peacefully. Of course this may not work all the time, in which case strikes against enemy position inside the city will have to carry out by all means.
I would consider urban battles as early stage of mopping up operation rather than part of main invasion phase because when a city is surrounded, PLA is already winning. Later stage of mopping up phase will be hunting down enemies hidding in the mountains.
Just like in Mariupol, PLA can take their time systematically clear sector by sector in a city until all enemy are terminated. Damages to buildings and infrastructure can not be avoided, and must be accepted.
A city under sieze would be under 24 hour surveillence by drones like CH-4/5, JDI types of drones, unmanned ground vehicles etc, to track all movements and activities on the ground and fortified positions inside buildings. Identified enemy positions will be terminated by all means.