"Under the DMs Guild program, you can publish D&D material that has no setting or uses the Forgotten Realms, Ravenloft, Eberron or Ravnica settings."
"When Gary Gygax penned the AD&D Dungeon Masters Guide, the world was
very different. The fantasy role-playing hobby was an entirely
different beast than it is today, for one thing. ... I also find it enjoyable to go back and read Gygax’s prose just to get a
feel for the kind of place he was writing from and the kind of audience
he assumed he was writing to."