There is no official way because the companies do not want to be all transparent. You have to find statements of the 3 companies.
Because of the WD Red SMR "scandal", heise (de) did some more research and asked Toshiba and Seagate. They said that their NAS HDD's do not use SMT. read here, in the section "update": https://www.heise.de/newsticker/meldung/Manche-WD-Red-Festplatten-fuer-NAS-verursachen-Probleme-4703116.html
That means of the dedicated NAS Hard Drives there are only these Disks using SMR:
WD Red WD20EFAX
WD Red WD40EFAX
WD Red WD60EFAX
me too, I've ordered a WD 4TB and have returned it now (it was within 30 days after purchase).