That is untrue, the IRS guidance for the 1099-B is consistent, but is not for other relevant forms/fields, the key one being 8949.
The IRS instructions are for negative numbers in parentheses for 1099-B, the form given to you by your brokerage. Your brokerage is following the IRS guidance they are given.
TurboTax doesn't fill out a 1099-B, they use values from it to complete your 8949. Instructions for 8949 do not say to enter negative values in parentheses (but don't explicitly bar it either). They are being instructed by the IRS that they will reject filed returns with a negative proceeds value. Intuit is following the IRS guidance they are given.
So while there are a number of ideas on how you can fix it yourself such as summarizing or switching the negative proceeds to zero proceeds and increasing the cost basis Intuit is likely waiting on more feedback from the IRS on their ambiguous instructions that have caused before coding that translation, potentially triggering audits, only to have the guidance changed again by the IRS.
