As I read the help,

F9 Calculates all worksheets in all open workbooks.

SHIFT+F9 calculates the active worksheet.

CTRL+ALT+F9 calculates all worksheets in all open workbooks,
regardless of whether they have changed since the last calculation.

CTRL+ALT+SHIFT+F9 rechecks dependent formulas, and then calculates all
cells in all open workbooks, including cells not marked as needing to
be calculated.

CTRL+F9 minimizes a workbook window to an icon.

Is there some way to force Excel to recalculate just one cell without
recalculating anything else?

I have a sheet that calls a VBA function from a lot of different
cells. If I put a trace or msgbox in the function for debugging, I
don't want it to run 50 times.