TurboTax's calculated "Effective Tax Rate" is a relatively meaningless number. It's simply income tax divided by AGI, Form 1040 line 14 divided by line 8b. It does not take into account your deductions or other taxes such as self-employment tax. It is definitely not your marginal tax rate which is the increase in your tax liability for each additional dollar of a particular type of income at your current income level.
To understand the differences between your 2018 and 2019 tax returns you must compare Forms 1040. Comparing TurboTax's Tax Return Summaries tells you nothing.
