The problem is the US has done a lot (though it's not solely to blame) to propel China up on the world stage, especially in the last decade+. We have given up a lot of our world leadership duties in many aspects and China wasted no time in filling any voids that we left behind.

This isn't just a Trump thing (though he has accelerated pulling the US out of leadership positions) but it goes back to the lack of response to the Crimea annexation (and Russia's continual pushing of it's Ukrainian boundary).

China has spent the last several decades smartly becoming more diversified in what countries they depend on, while at the same time making sure the whole world was heavily reliant on themselves. Due to that no one country can do anything to keep China in check, and in normal times that would be OK. However, the world has relied on the US to form global coalitions that would work together to push back against things like this, and now that the US has made it clear it will not work with anyone else (even allies), China knows that no other country has the influence to form such a coalition. That means it doesn't even need to be coy about what it's doing (as we are seeing with Hong Kong).

So yeah, I agree that in 2019 and 2020 the US and Eu/Britain couldn't have done anything meaningful, but what's happening right now is heavily caused by the US' pulling out of the world stage leading up to it.