@DawnC :
Apple (like every other software vendor) extols the virtues of their newest release. They describe Big Sur as "Bold new experience. Same Mac magic. Unparalleled power. Legendary ease of use. Limitless creativity. macOS Big Sur brings a refined new design that gives you even more of the things you love about Mac." and give more details at https://www.apple.com/macos/big-sur/features/
Intuit knew that it wouldn't make any business sense to compile TurboTax 2020 so that it would only run on Big Sur and later versions of macOS.
Most of the customers complaining in this thread are pointing out that it doesn't make business sense to compile TurboTax 2020 so that it would only run on Mojave and later versions of macOS.
