There's a utility called OpenCore Legacy Patcher described in the following article that will allow older Macs to install the latest MacOS Big Sur and therefore should enable users with older Macs to run Turbotax 2021 when it is released. I would suggest testing this first on a partition or separate hard drive from your current boot drive, so if it doesn't work it's pretty easy to undo without harming the current working configuration.
https://lifehacker.com/how-to-install-the-latest-macos-on-an-unsupported-mac-[phone number removed]
