It could be if Intuit was willing to compile TurboTax 2021 to include Mojave.as a deployment target.
But the answer is that Intuit has said that they won't do that. They've said that they will require macOS 10.15 (Catalina) or later.
Perhaps if enough of us contacted Intuit's corporate executives now (i.e,, before any work on TurboTax 2021 is started), Intuit executives could be persuaded to support as many versions of macOS as Apple's development tools will support as deployment targets .
