Brazil has historically been untrustworthy from a geopolitical standpoint. Russia is currently invading another European country. India could be stable, but they have a long way to go in terms of both development internally and on an international stage. China has essentially allied with Russia as they invade another country and is projected collapse in population to 800 million by 2100. And Saudi Arabia is soon to become nearly uninhabitable due to global warming and their main revenue stream is being phased out in many parts of the world.

The countries that are "worried" about the USD as international standard currency are mostly countries that are politically misaligned with the west or are developing countries that want to focus their reserve in more regional currencies to help insulate them from international crises. Any other countries that are shrinking their percentage of USD in reserve are probably doing so to diversify their "portfolio" like any sane person would that holds significant value in the stock market.

The USD may lose value in the next decade or so, but until there's a concerted effort by the EU,G7,UN, etc. The dollar will almost certainly remain the standard. It's a massive and stable market that's still projecting population growth into the 2100's.