I think the PRC government knows by now that the West, and even China's near neighbours, don't dare or don't have the capability to resist Chinese expansion. Tibet was annexed long ago; the Chinese military is now established across the South China Sea, having fortified most of the islands there, despite their being far from China and claimed by other countries, with hardly a peep from the US and no pushback. My guess is that there's a faction, at least, in the People's Liberation Army that calculates that sometime soon they might be able to overwhelm Taiwan with a fast, massive invasion and the US would make some symbolic bleats but would quite quickly accept the fait accompli. The Chinese have recently been pushing against India too. And of course they now hold strategic assets across the world, including seaports in places like Sri Lanka and Greece which, if the Chinese chose, could over time gently morph into naval bases. Stoltenberg is right to flag up the issue but whether anything serious will be done, remians to be seen.