Count occurrences of given character per cell

An alternative for one cell at a time (formula to be copied down):

=len(A2)-len(SUBSTITUTE(A2,"N",""))

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.