El Salvador didn't capture the entire BTC supply, as far as I know they managed to obtain less than 1000 btc. The US Government can't buy the whole supply either because it is being held by diamond hands who would rather die than sell their bitcoin.
Official data says that the number is over 1000 BTC, more precisely 1120 BTC after the last purchase, and since Bukele always buys dip, it is possible that this number will change in the coming days.
Overall, El Salvador's treasury holds 1,120 bitcoin, according to official data, worth nearly $66 million.
No one can buy the total supply not only because there are people who will never agree to the sale, but also because there is an unknown percentage of BTC that is irretrievably lost. In addition, 2+ million BTC has not been mined yet.