Right now, there's over $1B of the $1 coins just piled up in Fed vaults. By law, the Mint makes them, and the Fed must buy them (credit Treasury's account with the value in digi-FRNs). They thus live on the asset side of the Fed's balance sheet, never going into circulation because no one wants them. (note that coin and FRNs are fundamentally different monetary entities. Coin is direct Treasury currency, while FRNs and the digital forms are Fed liabilities created against assets -- those assets can be the very Coin Treasury currency, of course).
Take a gander at the latest H.4.1:
Go to Table 8, and note the Coin item. It is now $2.3B total. Over $1B of that is just the dollar coins that will never be used.