=LET(
 matchQA,ISNUMBER(IFERROR(SEARCH("qa",D2),"not qa")),
 matchTest,ISNUMBER(IFERROR(SEARCH("test",D2),"not test")),
 matchProd,ISNUMBER(IFERROR(SEARCH("prod",D2),"not qa")),
 whichEnv,
  IF(matchQA,"env_qa",
   IF(matchTest,"env_test",
    IF(matchProd,"env_prod","missing named env")
   )
  ),
    IF(whichEnv="missing named env","invalid env",ISREF(INDIRECT(whichEnv)))
)