The warning about losses not within the prescribed limits is referring to the way negative numbers were entered, possibly from an import.
There has been a change by the IRS starting with the 2020 tax returns that will reject any return filed with a negative number reported in the proceeds or cost basis fields for Schedule D. TurboTax is flagging these situations ahead of time before the return is filed in order to prevent the IRS rejection. Some brokers are still using the old convention for reporting negative values and have not updated their reports to match the IRS. You would need to go over your entries and find the negative numbers
See the discussion in this thread, IRS Instructions for Schedule D and for Form 8949. Any negative numbers need to be entered in parentheses.