my tweak

=LET(
  testedblank,XLOOKUP(wkg_lkup_arr,allquestions[number],allquestions[more2],"number not found",0),
  matchedstring,IF(testedblank=0,"",TEXTAFTER(testedblank,"is incorrect because ",1,,,testedblank)),
  IF(matchedstring=$M3:$M109,"dupe",matchedstring)
)