Your error seems slightly different to mine and that of the original poster, but perhaps the root cause is the same. Namely, that Turbotax may not be populating the previous few years losses correctly in the Form. (i.e. the boxes shown in the screenshot above for 2018/2019/2020 etc. ) If you can find those values from your 2020 return / worksheets then you might be able to enter them manually into the form and proceed.
