Rental Property Fire Loss, how to report on taxes?

It's a 2 year old post. But I'll respond anyway since the answer still applies to the 2021 taxes.

expenses incurred in 2019 exceeded rental income.. can i write off remainder in 2020?

No. Not directly anyway.  It is very common for rental expenses to exceed rental income each and every year you are renting the property; especially if there's a mortgage on it. When you add up the deductible expenses of mortgage interest, property taxes, insurance and the depreciation you are required to take, those four items alone will almost always exceed the total rental income received for the tax year. Add to that your other allowed expense deduction (repairs, maintenance, etc) and you're practically guaranteed to show a loss on the SCH E line 26.

Beginning in 2018, excess losses can be claimed and deducted from "other" ordinary income up to a maximum of $25K, if certain conditions are met. Any other loss is just carried over to the next year, where they can be deducted *if* you have the rental income to deduct it from. That probably won't happen. So it's rather common for your carry over losses to increase with each passing year. You will not be able to "realize" those losses until the tax year you sell the property. In the tax year you sell the property all carry over losses are fully deductible.