As for Taiwan, it's an unknown and if you claim otherwise, you're doing it based on nothing. Biden has clearly and repeatedly stated that the US would defend Taiwan. Not saying the US actually wants to, maybe it's just a deterrent. However, if China does attack and the US backs off, that would mean the end of American supremacy regardless.
NPR hosted the former commander of NATO who called for the US to enforce a no-fly zone over Ukraine, to include shooting down Russian jets. Numerous Senators and Congressmen backed one as well.
https://www.npr.org/2022/03/03/1084310587/former-nato-comman...
And he was rebutted by the White House when it looked like he meant that the US would intervene militarily
No-one doubts that the US would help, e.g. by supplying intelligence, weapons, etc. as they do now. But they would not send troops and they would not engage (nice word to mean 'attack') the Chinese.
> Most likely the US would intervene militarily at some level with sea and air attacks
That's extremely unlikely to inconceivable because, again, the USA are not going to start a war with China because there's no path to winning, only to nuclear annihilation.
Both sides know that. Both sides will not attack each other whatever happens.