Yesterday I was at the beach. It was about 4-6 feet. I don't think it gets much bigger than that in the Taiwan Strait and, based on my personal experience, I don't think that would stop a tank.
Taiwan does use tanks for beach defence. Its older M-48s and other Korea-Vietnam era American tanks are assigned to act as moblie bunkers and fire on incoming ships and tanks. Since these tanks wouldn't be of much use beyond that anyway that is a good way to use them. But it would be a waste for a modern MBT. I'm sure and MBT could sink a ship, so lets stop arguing about that.
Here's a good historical example-The Battle of Kuningtou. In 1946, after the Nationalists had withdrawn to Taiwan, the PLA attacked Kinmen, as a stepping stone to Taiwan itself. In a remarkable feat for a force with no real navy, they were able to thousands of men on Kinemn. The Communists were slightly outnumbered by the ROC forces, as it would likely be in the initial hours after a landing by the PLA on Taiwan now. After overcoming the beach defences and advancing under the cover of mainland artillery, the PLA troops were met by a large force of ROC infantry and American made M5A1 Stuart Light tanks. Without many anti-tank weapons the Chinese were unable to stop the attack and were driven back to the water's edge, or into surrounding villages and hilltops. The ROC 18th Army was able to do to the PLA what the Germans were unable to do on D-Day. They exploited the gaps between landing forces with armoured counterattacks and caused the operations after the initial landing to become fights for survival, not coordinated advances inland. The next day more PLA troops landed, but did not find and organized beachead, only pockets of PLA troops fighting for survival against armoured ROC attacks. The second wave was decimated on the beaches with the help of the ROCAF and ROCN, and the next day all surviving PLA troops on Kinmen surrendered. The "moral" of the story is that tanks help would help to transfer momentum to the Taiwanese side in a modern invasion of Taiwan. Fun fact-The M5A1 tanks that the ROCA had on Kinmen were used as steamrollers against PLA human wave attacks after the ranout of ammunition.