In an effort to get you as many credits possible, TurboTax automatically claims any credits that it thinks you are eligible for. If you worked, but have a low income, TurboTax will claim the Working Income Tax Benefit (WITB), which is a refundable tax credit for people who work, but don’t make very much. However, students are usually not eligible for this credit, so when you tell TurboTax that you have tuition, then the WITB is removed if you no longer qualify for it.

https://www.canada.ca/en/revenue-agency/services/child-family-benefits/working-income-tax-benefit-wi...