Return the software that you purchased for a refund.
TurboTax for Mac only supports -
macOS Monterey 12 or later (macOS Big Sur 11 not supported)
- Specific macOS: macOS Monterey 12, macOS Ventura 13, macOS Sonoma 14
If you wish you can use the TurboTax online editions - https://turbotax.intuit.com/personal-taxes/online/file-your-own-taxes/
