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 regarding:
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 one of our upcoming software updates. It will be found when you enter your T4. Scroll down to the bottom of the T4 where you will be asked about working from home.
However and unfortunately, you may come across locked forms, or receive a message saying that forms aren’t finalized when using TurboTax, you will not be allowed to complete the filing of your return. Please see the link below for more information.
Is this form available on the online version of the application? I can't find it.
Edit: Found it it comes after the T4 import. You can search "Employment Expenses" under the Find on the top right. I can't delete this.