rjnjr3181,
I think you meant Tax divided by AGI and Tax divided by Taxable Income in your post.
TurboTax doesn't use Total Tax (2020 Line 24) to calculate Effective Tax Rate, instead they use Line 22 (2020) divided by AGI (Line 11). For some unknown reason they exclude Other Taxes (Line 23) from Schedule 2. This excludes the 3.8% tax on investment income. I think a better measure of Effective Tax Rate is Total Tax (Line 24) divided by AGI.
Obviously, the effective tax rate can be defined in various ways. I suppose it comes down to what is most useful for the particular situation.
