TurboTax minimum system requirements for Mac - https://ttlc.intuit.com/community/system-requirements/help/minimum-system-requirements-for-turbotax-mac-software/01/25609
If your Mac OS does not support the TurboTax software for tax year 2020 -
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 -
https://turbotax.intuit.com/personal-taxes/cd-download/order-status/
You can use the TurboTax online editions for tax year 2020 - https://turbotax.intuit.com/personal-taxes/online/
If your computer does not meet the system requirements for desktop software and cannot update to do so you have two options to use TurboTax for 2020
Buy a new computer
Use online TurboTax instead of desktop
If you cannot use the downloaded version because your system is not up to par and you will not be buying a new computer then you can still use the ONLINE version ... if you already bought the CD/Downloaded version put in for a refund of the fees paid as they cannot be transferred to the Online product.
https://turbotax.intuit.com/personal-taxes/online/
Go to this TurboTax website to request a refund for the software purchased from TurboTax - https://support.turbotax.intuit.com/forms/refund-request.jsp
If you need to switch to the Online version you can transfer from 2019 into the Online version. If you used the Desktop program last year here's how to transfer into the Online version, expand the blue link if you used the CD/download last year. You will need to have the filed ending in .tax2019 on your computer. Transferring from last year will clear out anything you have entered for 2020 and you will have to start over.
https://ttlc.intuit.com/community/entering-importing/help/how-do-i-transfer-last-year-s-return-into-turbotax-online/00/25953
If you used the Desktop program before you may not like the online version. It has less features and no Forms Mode. You can only do 1 return. Your return is only saved online so be sure to save both the .tax2020 data file and the pdf file to your computer when you are done. In case you need to amend it in the future or if you need a copy to get a loan or something. You might not be able to access your online return when you need a copy.
Mac System Requirements. For 2020 you will need macOS Mojave 10.14 or later
https://ttlc.intuit.com/community/system-requirements/help/minimum-system-requirements-for-turbotax-mac-software/00/25609
Online system requirements
https://ttlc.intuit.com/community/system-requirements/help/turbotax-online-system-requirements/00/25787