NA function
Returns
A "not available" error.
  Returns an #N/A error ("not available"). As the ISNA function returns whether
  its parameter is an #N/A error, ISNA(NA())ISNA(NA()) returns TRUE.
  Lookup functions like XLOOKUP return #N/A errors
  when a value cannot be found. The ISNA function may be used to detect the
  #N/A error specifically.
This formula returns TRUE, because the sought value, 10, is not part of the { 20, 30 }{ 20; 30 } lookup array given to XLOOKUP:
  ISERR is the opposite of ISNA, meaning that it detects all errors
  except for #N/A errors. Consider this formula:
  The preceding formula returns TRUE if the value of Field2 is 0 or
  blank, resulting in a #DIV/0! error, but it returns FALSE if the
  value resulting from the Field1
  /
  Field2Field1 / Field2
  calculation cannot be found in the lookup array.
Examples
Returns TRUE, because the sought value, 10, is not part of the { 20, 30 }{ 20; 30 } lookup array given to XLOOKUP.