Hard to say how redundant this will be with what is in the new DMG, but the go-to would be the 1983 World of Greyhawk box set, which is $9.99 on the DMsGuild: it includes all the material from the original 1980 Folio including the classic map, with a lot of expansion material. It is the only Setting product Gygax was involved with, other than Adventure modules, which the box set locates on the map in the booklet (note: there is a lot of...Gygax...stuff in here that I expect the new DMg to fix).
TSR would make other stuff later, but usually their heart wasn't in it, and the DMG seems to be a timeline reset to the box set (as Ghosts of Saltmarsh was) so even most of the latter metaplot tinged stuff would be of mixed usability and very...2E:
World of Greyhawk Fantasy Game Setting (1e) - Enter the WORLD OF GREYHAWK... ...A world where bandit kings raid from their remote stronghold; ...A world where noble
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