Up to 2.82 it is mentioned.
2.83 - 2.93 it is not mentioned anymore
In the documentation of the Mist Pass in the World Settings up to 2.82 it is mentioned to enable the Mist Pass to see these settings, from 2.93 forward it is not mentioned anymore. For new Users this can be confusing, because they do not know why they do not see the settings the documentation says to be there.
With a description change at that time, the following Paragraph was in the old documentations and than dropped.
"Shown when the Mist pass is enabled. Mist values will range from 0.0 - 1.0 and are available from the Render Layers node."