The notes in the current beta sample project say that sorting in the Outliner (by clicking on a header) does not work currently except in Collections and multiple selections.
I can’t get sort to work at all in multiple selections. It works in Collections on standard fields but I tried to sort by a custom date field in a Collection and even though the up and down arrows/chevrons change direction on click the items in the Collection do not change by reference to the date that is entered for each. Essentially nothing happens other than that the arrow/chevron in the header changes direction (up or down).
I don’t know whether this will be solved automatically when the full functionality of sorting (beyond Collections and/or multiple selections) is implemented or whether there is a more substantial issue with custom field sorting or at least date field sorting.