You can carry back net operating losses beginning in tax years 2018, 2019, and 2020 for five years.
However, a loss on Form 4797 does not automatically generate a net operating loss (NOL).
TurboTax does not calculate NOLs so you would have to do the calculation manually.
See https://www.irs.gov/publications/p536#en_US_2019_publink1000177328
