" you can't amend 2018 because the method you used was an impermissible method requiring filing form 3115 for 2020 to catch up. "
You mean its not easy/possible to do this in TurboTax because it was different each year, and for 2020 I would need to file 3115 to be able to consider the final(right) depreciation. If my understanding is correct, then I only need to worry about the 2020 return and file it, but use another service (probably a local CPA) to file the 2020 return including the 3115, right? The 3115 would be based on calculations that consider differences between 2018, 2019 and 2020, something like 3 different calculations all in one
