Trump is oblivious to the fact that BRICS is now a bigger economy than the G7. The US is no longer an essential part of the global economy.
Increasing trade outside of the dollar is the only way countries can protect themselves from economic coercion by the US. In particular, China can obviously see that the US will go after them the same way they did with Russia. So, it would be suicide to agree to tie their global trade to the dollar.
Meanwhile, China also happens to be a bigger trade partner than the US for most of the world. So if it comes to choosing between the US and China, it's not really much of a choice. Especially given that China exports things people actually need, while the US barely has any manufacturing industry left accounting for less than 15% of the overall economy. The US is a big market, but it's not essential the way China is.
It kind of reminds of a past job I had where a co-worker recently contacted me and told me he quit. The general manager was abusing his position and disrespectfully issuing out orders and demands to employees that already had 10 different things going on at the same time. The idea of not being a total hegemon just didn't seem to physically register in his brain and both of us ended up telling him to fuck off and leave him short staffed for Black Friday.