You can’t ever get any concrete proof for a broad statement like "China focuses on economic growth first and foremost, rather than militarization and forceful expansion". But the best proof you can get is this precise situation. Of course even looking at it from a purely militarist perspective attacking Taiwan is very bold. Considering it’s geography and the potential of third party‘s (USA) intervening militarily.. but hey, Putin faced similar concerns and didn’t give two fu*ks. The main reasons Taiwan is not under attack yet are of economic nature. It’s semiconductor monopoly that China depends upon and the possibility of Western sanctions crippling China‘s export business, as well as the possibility of Western companies pulling out of China. Both of these Xi does not want to have under any circumstances, as it appears.