Sorry---if you cannot upgrade your Mac's OS to meet the system requirements for the desktop download then your remedy is to use online software. You cannot pay for online using the license code. Seek a refund for the download software and pay the current fees for online if you want to use TurboTax.
To request a refund for a TT product
https://ttlc.intuit.com/turbotax-support/en-us/help-article/intuit-refunds/request-refund-turbotax-p...
ONLINE 2024
https://turbotax.intuit.com/personal-taxes/online/
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**