China does not care for the west as a trading partner much more than as a stepping stone to reach elsewhere. The west uses economic advantages to arm twist domestic Chinese policy. If they have their grip on Africa, Asia and S. America who cares about the fading west?
And the USA right now is vital for continued world peace and stability as a superpower. There many many nations that owe their geopolitical stability right now to the US being the sole super power.
China has sheer volume but being maybe a third at most their population size the US dominates many things still. Technologically they're still behind in military appllications. The US woud squash China in a heartbeat in both conventional and Nuke warfare. And you have to undetstand how much SK and Japan (both important UK allies btw) are important to the US. Their loss too China will happen only after losing WW3. These are one ot many reasons why both China and Russia are working hard to dismantle the US and UK from the inside out as well as sow discord between them. UK fought with US in both Iraq and Afghanistan!!! Many brits died in America's wars already.
China and Russia (with many smaller countries who are growing more resentful of the advantage we get having the dollar as the world reserve currency) are actively trying to undermine the dollar (let’s hope they fail, or that it takes a long time!) but they probably view the U.K. as a trading partner and as much as possible be cordial with.
England is done with being the world mono polar superpower so they don’t show up strategically as a real adversary.
For financial and ego reasons, the USA is trying to hold on to its status (although by over using tariffs and sanctions, we are being incredibly clumsy - we need to get our act together!)