His threat was directed at countries in the so-called BRIC alliance, which consists of Brazil, Russia, India, China, South Africa, Egypt, Ethiopia, Iran and the United Arab Emirates.
Summary
Trump has threatened 100% tariffs on BRICS nations (Brazil, Russia, India, China, South Africa, and others) if they pursue de-dollarization efforts, including creating a new currency to challenge the U.S. dollar’s dominance in global trade.
Trump warned these nations could lose access to the U.S. economy.
BRICS members, frustrated by U.S. financial dominance, have explored alternatives, with Russia advocating for a new payment system to bypass sanctions.
Analysts say the dollar’s global reserve status remains secure in the near term despite these challenges.
Euro overtaking the dollar as reserve currency in 3, 2, 1...
Thing is: Much of the volume of USD-denominated trade is habit and inertia, it's a convenient unit of transfer and thus banks keep reserves of it to make transactions with. It took the US blocking a payment from a German customer to a Danish tobacco retailer for banks to switch Euro<->Kroner transactions to not go via USD (Those were Cuban cigars) as standard operating procedure for banks very much involves "don't fix it if it's not broken".
Thus: The more you stir the pot, the more people want to get away from your complications. On top of being a convenient unit of transfer the Euro is also backed by a similarly-sized economy as the dollar and on top of that much more price stable against that economy: The Fed is perfectly willing to inflate the dollar to influence e.g. employment, while the ECB is committed to price stability, rather telling member states to devalue internally if that's what's necessary the prices shall stay the same.