If you took it off the rental market to list it for sale, then during that period, it is not a rental property and no rental expenses can be deducted.
It can be considered as a second home and you can deduct mortgage interest and property taxes as itemized deductions in the personal section of your tax return.
If this rental property was available for rental until you sold it, you can deduct the mortgage interest, property taxes and other expenses as rental expenses in 2020 even if you had no rental income.
There were no renters in it because it was vacant while being listed for sale. Does this mean it was still a rental during that time period?
If you took it off the rental market to list it for sale, then during that period, it is not a rental property and no rental expenses can be deducted.
It can be considered as a second home and you can deduct mortgage interest and property taxes as itemized deductions in the personal section of your tax return.