Technically, China doesn't want to annex Taiwan per se because they already have the view that they "own" Taiwan. Thus, no annexation needed as Taiwan is just a "rebellious" providence that just so happens not to listen to the CCP. To annex means to acknowledge that Taiwan isn't under China's own control ab initio, thus no One China exists, but rather two Chinas exists., which contradicts their position. Taiwan also has the One China policy as well and as such it becomes a big elephant in the room that doesn't get acknowledged in day to day life unless saber rattling or some political maneuvering is needed.