The TurboTax online editions for tax year 2020 should be available in early December - https://turbotax.intuit.com/personal-taxes/online/
The TurboTax desktop CD/Download editions for tax year 2020 are available now - https://turbotax.intuit.com/personal-taxes/cd-download/
Although the downloaded program is available now with the online following sometime in December they are NOT fully operational programs ... they are only beta versions. The final program and the state programs are never fully operational until late January at the earliest.
ANY tax software released by any company prior to about January 15 is only released for marketing and market share. No program is complete and ready to file until the IRS approves their final forms and then individually reviews each program's implementation of the form. And some tax situations aren't able to be filed until February or March, again mostly due to IRS delays.
Now, it would be better if the updates that were easy to do were done in advance. But that may not fit the program workflow. For example, if the MAGI calculation is part of the module or subroutine for form 8606, the programmers may decide not to update any part of the 8606 subroutine until the actual form and instructions for 2020 are released by the IRS and then reprogram the entire module all at once.