Why? Argentina is a big asset for China and BRICS. Out of Latin America, Argentina is the only country that will be a forever enemy of the west and US because of the Falklands issue. Argentina is always kept weak and not given military tech by the west due to falklands. This creates resentment in Argentina and is a perfect foil for China to give its own support and also fuel Argentina's nationalism for Falklands.I had the same opinion pre this year brics meeting but it seems China and Russia have India under control.
I'm more worried about Lula and Brasil. Argentinia as a candidate was a big L for brics in the PR department and accidental big W not having to deal with Argentinia.
Just because Argentina elected a far-right candidate does not change its long term trajectory as potential Chinese ally against US and UK due to falklands issue. Argentina is also quite far from US and safer from US military domination, which means there is a chance China could get bases in Argentina in the future.
Mexico is another long term asset which will always feel resentment due to US taking Mexican land in the past. The more powerful they get, richer they get, the more they will want to take those lands back and also have revenge. They will also feel threatened due to US power. That again gives China the opportunity to gain foothold. Do to US what its doing by using Japan, Vietnam and other Chinese neighbors.
Argentina and Mexico are long term assets of China in Latin America to keep US busy and also gain foothold in Latin America.