Why did the Turbo Tax program substract my penalty fee for the underpayment of taxes from my federal tax due for 2020? It should be added or allow IRS to bill me.

If Turbo Tax doesn't automatically fill it out you can add it yourself.  You can go to Federal Taxes tab or Personal tab, under Other Tax Situations and select Start by the Underpayment Penalties. You will answer a series of questions that may reduce or eliminate the penalty. Or you can elect to have the IRS figure the penalty for you.  It's form 2210.

It's under

Federal or Personal (for Home & Business Desktop)

Other Tax Situations

Additional Tax Payments

Underpayment Penalties - Click the Start or update button

And even if you or Turbo Tax adds it on line 24 it is only an estimate.  It's common and expected for the IRS to bill you for more depending on when they actually get your payment.  Or even send you a refund for some.