To correct your situation, you would have to say YES instead of saying NO on the right screen after you have entered Employment Expenses as described below.
For more information, please follow these steps:
For the flat rate method to be activated in TurboTax, you enter your T4 and scroll down to the bottom where you will be asked: Will you claim employment expenses for working at home due to COVID-19 for income on this T4? NEW! You will then click on Employment Expenses found lower in the menu on the left side of the screen to then answer yes on the right screen. On the Employment Expenses Profile page, check the option: I didn't receive either form from my employer. On the next screen Check the flat rate method and enter the number of days you worked from home.
You have now used the flat rate method to claim employment expenses.
For more information, please follow these links
How do I claim home office expenses?
Am I eligible to claim employment expenses due to COVID-19?
Employment Expenses Tax Info Centre
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