Count occurrences of given character per cell
Solution 1:
An alternative for one cell at a time (formula to be copied down):
=len(A2)-len(SUBSTITUTE(A2,"N",""))
Solution 2:
I don't know if this is gonna help but let's say you have those strings in range A2:A6 and you enter
=ArrayFormula(LEN(REGEXREPLACE(A2:A6, "[^N]", "")))
in B2, that should output the N count for the whole range.