I had asked the user some time ago if he had
C:\Users<user>\Downloads
and indeed he does:
so I concluded that that was not the issue.
A small test program sent to him now, however, reveals that while not nil, Downloads does not exist as far as Xojo is concerned, so that any child I designate will be nil.
Pretty sure it’s a OneDrive thing. Easy to fix now that I know the root cause. Thanks to all.