You should seek guidance from a local tax and/or legal professional.
However, you should most likely file a return for the year of the sale to record the loss. Nevertheless, the loss will remain with the estate until the final return is filed (at which point any recognizable losses can be distributed to the beneficiaries).
You do not have to file for any tax year during which the estate had gross income of less than $600.
See https://www.irs.gov/instructions/i1041#idm140229151947712
