How do we claim the flat $400 that’s available now? 

Expenses related to a home workspace can be included on line 22900 but there are considerations to review with the new allowances and possibilities available due to Covid 19 this year. 

Here are Canada Revenue Agency links with information to be reviewed if needed.

canada.ca

Home office expenses for employees - Canada.ca

As an employee, you may be able to claim certain home office expenses on your personal income tax return: What is eligible, types of claims, and how to claim.

canada.ca

Eligibility criteria - Temporary flat rate method - Home office expenses for employees - Canada.ca

See if you qualify for claiming home office expenses using the temporary flat-rate method.

Note: If using the form method, one of the forms required, the T777S-Statement of Employment Expenses for Working at Home Due to COVID-19, for the flat rate method will be available on our future software update.

Thanks, but what does that mean when I’m using TurboTax online? What do I have to check off to get the option to appear? (I will be claiming the straight $400 with no additional documentation, if that matters. 

On the next software update, on Wednesday, February 3rd, we will integrate the T777S-Statement of Employment Expenses for Working at Home Due to COVID-19. You will be able to enter the $400 flat rate employment expense at the end of the T4 entry. Here, in your online version, you will answer a question about working at home.  Please look for our upcoming  FAQ on our TurboTax Canada website.