What does it mean when Turbo Tx says to enter any withholding from payments you received in 2019 that you haven't entered elsewhere.

[CatinaT1]

This means any money withheld for taxes from income you received or any estimated payments toward income tax that haven't already been entered.

[jmcc]

Usually amounts withheld will come from W-2 forms that employers provide.  Other forms, 1099R for example, will also list amounts withheld.  Turbotax asks for these as it goes through the various sources of income.  This is a final question to make sure that all amounts withheld from every income form has been entered.