TurboTax is correctly calculating MAGI for the purpose of the exclusion of unemployment compensation. It's precisely following the procedure provided by the IRS:
https://www.irs.gov/forms-pubs/new-exclusion-of-up-to-10200-of-unemployment-compensation
The American Rescue Plan Act of 2021 which added subsection 85(c)(2)(B) to the tax code to implement this exclusion includes subsection 85(c)(2)(B) which stipulates that unemployment compensation is not to be included in MAGI for this purpose.
