I spoke with Microsoft support that told me that data validation via a named
list not working is a "Known issue". From that I assume it will be fixed
shortly. Can anyone enlighten me as to when this first update might be
forthcoming?
Nobody who knows can tell you (assuming that anyone does yet).
If you look at what's happened in the past, the first bug-fix release
for major applications have typically been released sometime in the
first six months or so after release of the original upgrade. That's not
a prediction, of course.
Note that data validation via a named list works for me as long as the
list is on the same sheet as the validation cell.
If the list is on another sheet, the Validation itself works, but no
dropdown is displayed.