I've got a table of British WWII aces:
Pilot | Squadron | Kills
John      2nd        8
Mary      2nd        5
Alex      7th       12

I make a Report, and group the data by Squadron:
Squadron |Pilot | Kills
2nd
          John      8
          Mary      5
       Tot. kills: 13
7th
          Alex     12
       Tot. kills: 12

Under "Sorting & Grouping" I set "Field/Expression" to [Squadron], and
I can set "Sort Order" to either ascending or descending.  Also, in
the [Squadron] footer I  put a text box that calculates total kills
per squadron.

Problem: I want the squadrons to be ordered by total kills, not by
squadron name.  "Sorting & Grouping" will only let me order groups by
the group field, ascending or descending.

Note: This problem is not about sorting records, it is about sorting
the groups of records.  Perhaps the answer involves an intermediate
query or Visual Basic?

I don't know the details, but yeah, you'll have to make an
intermediate query to generate the totals, then use that query in your
report.