TurboTax minimum system requirements for Mac - https://ttlc.intuit.com/community/system-requirements/help/minimum-system-requirements-for-turbotax-...
Go to this TurboTax website to request a refund for the software purchased from TurboTax - https://support.turbotax.intuit.com/forms/refund-request.jsp
Use this TurboTax website to check your orders and payments -
You can still use the TurboTax online editions for tax year 2020 - https://turbotax.intuit.com/personal-taxes/online/
How to transfer the 2019 tax data from a computer to the 2020 online editions - https://ttlc.intuit.com/community/entering-importing/help/how-do-i-transfer-last-year-s-return-into-...
Sorry you either need to upgrade your Mac to a newer OS or get or borrow a newer Mac or use a WIndows computer. Or you can use the Online internet version this year. If you can't run Turbo Tax you can get a refund. https://support.turbotax.intuit.com/forms/refund-request.jsp