When inputting 1-5 V, what’s the difference between selecting 1-5 V for the input range setting, and selecting linear scaling and using a 6 V range?

1-5 V and linear scaling both have the same measurement accuracy.
With the 1-5 V range, you can use low cut.
For the 1-5 V range, set the span in the allowable range. Ensure that you set it so that scale left < scale right.