Yes, Biden has said that in one way or another, but it seems that when he does someone else near him walks it back a little--which in Abe's eyes makes the statement less clear/forceful than he would like.
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Ukraine should give the CCP pause. Tho Russia may have botched it, even invading/toppling a country right next door--that you can drive to, and that you effectively almost have surrounding land border to begin with--may not go as planned. And their military, at least up to a couple months ago, would have gotten pretty high marks.
Crossing water to do something similar (to get to Taiwan) is a very different ballgame, and tho China has missiles and an air force, and could undoubtedly blow lots of things up, its navy is not its strong point. Even their invasion of Vietnam went badly (which could have been a lesson for Russia in Ukraine)--a supposedly overwhelming force that was severely bloodied. That was decades ago, and while there's been a lot modernizing and money spent, China's military is otherwise untested (I don't think skirmishes in the Himalayas count). As Mike Tyson said, everyone has a plan until you're hit in the face.
Similarly, the Koreas. On the one side, even with nukes, Kim should realize (maybe does?) that conquering/assimilating the south is just not ever going to be possible. And on the other, hopes that the north will somehow collapse, or that a war would be quick--or that a 'decapitation' strategy might work--should be taken with a grain of salt. This should comfort China, since what it looks at as its DPRK "buffer" isn't going to just disappear.
What has happened in Ukraine also shows the importance of practice. Eg, US/ROK yearly military exercises, along with anything with Japan/US. It's one thing to have x-number of hypersonic missiles and stealth aircraft, managing those in a war is something else.