People repeat this a lot and I don't think they've ever actually been to Japan, or outside of the big cities. Go 30 minutes outside of Tokyo and you can count on one hand the number of gaijin you'll see. Not saying the situation won't turn worse, but the state of immigration in the US or any other major Western country to that of Japan is incomparable. Not to mention their immigration laws, despite what you may have heard, are actually pretty strict if you want to STAY in Japan for longer than six months. Just ask the trannies who tried to emigrate there when Trump won.
Furthermore on the China issue, Japan has recently begun remilitarizing (slowly) specifically because they don't believe the US can protect them against China any longer. They've been ramping up their navy and trying to get JSDF recruitment up. There's an Economist article about it that I'd dig up somewhere, but I'm phoneposting and it's paywalled. This was during Biden's term, of course. Anecdotally all the Japanese people I've talked to HATE the Chinese tourists and immigrants because many of them either suck at Japanese or don't bother to even learn it. Sound familiar?
So yes, I do think Japan and the US would see eye to eye on the China question. I think Japan is heading in a direction that could turn it into another shithole like most of Europoorstan, but it's a ways off yet.