I contributed 100% of my RMD to charity. Why is it listed as taxable income?

Did it go directly form the plan administrator to the charity?

A QCD that is a direct trustee-to-trustee transfer by the trustee of your IRA to the trustee if the charity is reported when you enter you 1099-R.

If over age 70 1/2 the interview will ask if this was a RMD and then ask if you had a transfer to a charity.   Enter the amount and it will subtract that from the taxable distribution on line 15a on the 1040 form with QCD next to it.