On CSA Form 1099R the Taxable amount is lower than the Gross distribution. Why does TurboTax not enter the lower Taxable amount on the total income section?

TurboTax is not listing your TAXABLE income, it is just a picture of what money came in for you for 2023. 

You can look at your 1040 to see what is being reported on line 5a (total) and 5b (Taxable) 

To View

For TurboTax Desktop, switch to Forms (top right) 

TurboTax Online:

Select Tax Tools on the left side-bar

Select Tools from that drop-down

Select “View Tax Summary” on the TOOLS CENTER screen

Select “Preview my 1040” which now appears on the left side-bar