Gary of all the ways to treat PPP forgiveness that I have seen and read, an M-1 adjustment is I believe the correct method. Question - in the TT business software I suspect that you went to the "Forms" section and went to the M-1 worksheet and in the income section under the heading "Expense Items" entered PPP Forgiveness (under Other Permanent expense items) for the $$$ value under the Per Books Column with nothing in the Tax column (its grey'd out) thereby creating your book / tax difference. I was able to balance my balance sheet 100%, the book income was correct to include both PPP Forgiven loan as income and associated expenses it was used to pay and c. my taxable income was correct to include the 50% disallowed for meals as well as now the PPP forgiveness.
