Nothing special here. Enter your rental income for 2020 as $0 and that takes care of the income section entirely. Then enter your rental expenses, and press on.
Take note that it is NOT common for rental property to actually show a taxable profit anyway - especially if there's a mortgage on the property. Since your rental expenses can only be deducted from rental income, and since you have no rental income to deduct those rental expenses from, your "unallowed" rental expenses will be carried forward to the next tax year and included in that carry forward amount will be the total of all unallowed losses (if any) from all previous tax years.
You cannot deduct a loss on your return due to income that you never received, no matter the reason.
If your rental room was being advertised and available for rent during 2020, then it is still considered a rental property and you can deduct expenses related to that portion of your home that is the rental property. This could generate a loss on your tax return since there is no income being reduced by the expenses.
If you did not advertise the room for rent because you did not want a renter due to Covid-19, then you did not have a rental property during 2020 and you cannot deduct any expenses related to it.
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