Why not have tax withheld by the brokerage when you take the distribution? That's the simplest way to cover the tax, and it avoids possible additional calculations and forms that might be needed to avoid a penalty when you file your tax return.
There is a distinction between selling the shares and taking the distribution. You can sell stock in your IRA and leave the proceeds of the sale in the IRA. That would not be a taxable transaction. You incur the tax when you take money (or stock) out of the IRA.
You mentioned making the payment "when I sell," but you also said "before 12/31/25." Before December 31 might not be good enough. You have to make the payment by the payment date for the quarter in which you take the distribution. For example, if you take the distribution in June, July, or August you have to make the payment by September 15 to avoid a penalty.
If you use Direct Pay, be sure to specify that it's an estimated tax payment for 2025.
