Yes, those are possibilities. Plus anything that was changed because of COVID changes to tax law. I would suggest doing a line-by-line comparison to see what’s different between the two returns if you want to understand what your particular differences are.
Expanding on aj’s advice, if you really want to see the change in efficiency, I would take your 2021 numbers and run them through the 2020 tax program, and take your 2020 numbers and run them through the 2021 program. You can then compare the 2020 tax program results to see how the efficiency changed due to income changes from 2020 to 2021. You can also compare the 2021 tax program results to see the efficiency change. I wouldn’t expect to see the same results from the two software programs due to the effect of income-based tax provisions.
Ira