It is not just "TurboTax" that isn't using the amount from Box 52, CRA only allows the portion the employee contributes to the RPP as shown in Box 20 to be used as a deduction. On the T1 General Tax Return, Box 52 is a box that is a "side box", not included in the calculation to reduce your Net Income.
I've attached an example of a T1 General Tax Form that shows a 50/50 contribution between the employee/employer, and you can see that only the "employee paid portion" is used to arrive at Net Income.
Here's the CRA information on Line 206 - Pension Adjustment: https://www.canada.ca/en/revenue-agency/services/tax/individuals/topics/about-your-tax-return/tax-re...
