What is the difference between IFERROR and IFNA?

IFERROR catches every error type — #N/A, #REF!, #VALUE!, #DIV/0! and the rest — and substitutes your fallback.

IFNA catches only #N/A.

With lookups, IFNA is usually the better choice: a missing match is expected and worth handling, but a #REF! is a real bug you want to see rather than hide.