The foreign exchange reserves held by the national central bank are called reserve currencies, usually US dollars and Japanese yen.

Because these countries have a solid economic foundation, they are regarded as reserve currencies. Simply put, these currencies are preserved.

Gold has always been regarded as a precious metal to preserve value.

The purpose of a country holding these is to avoid risks, buy when the economy is good, and sell when the economy is bad (or political needs) to stabilize its currency interest rate, with the aim of stabilizing its economy.

Simply put, holding reserve currency and gold is to avoid risks. It is still a political need.