If the property was not 'Available to Rent' in 2019, you are correct that you could not deduct the Property Tax as a Rental Expense.
Since you owned the property, though, you can enter it as an Itemized Deduction.
Don't delete the Rental. Again, you are right that you will be able to claim all the Carryover amount when you sell it or 'stop using it for business'.
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