The sunset is easy to predict ... the oldest year is pushed out by the incoming year. The switch happens when efile closes at the end of October for the current year program. Only the last 4 tax years are supported ... the current filing year + the 3 years prior ... note the page where you can buy the prior year program has only 3 tax years to choose from (2020, 2021, 2022).
https://turbotax.intuit.com/personal-taxes/past-years-products/
Right now 2020 will be gone when the 2024 program goes live in November because 2023 moves to a prior year status. This stepping down has been the same for the at least the last 20 years that I know of & I don't see the policy changing any time soon.
