I've seen answers to this from the past (protect sheet but leave cell
unlocked) but this does not help my problem.

I have spreadsheets used by many staff where it is essential to enter a + or
- symbol. Excell always treats these as a "function" instead of simply
"text" no matter if the format is set for "text."

Yes, you can enter a ' before the symbol to force "text" mode -- a very old
protocol -- but surely there's a way to make Excell accept entries as text
and leave it that way???