What is likely happening is your age amount deduction on Line 30100 of the tax return is being reduced due to your Net Income being over the threshold amount of $38,508. TurboTax works out this calculation for you and enters the reduced amount on this line.
You can find the calculation by going to the CRA link: T1 Income Tax Package for 2020, choose your province, then click on Worksheet For The Return. If your income exceeds $89,422, you will lose the Age Amount deduction entirely.
Hope this helps you to understand that calculation. Happy tax filing!!
