For what setting? The world books discuss various deities for Dragonlance, Eberron, Realms and Exandria, and the GH deities get a name drop in the DMG. Most other settings have either no religion (Athas) or no fixed ones (Planescape, Ravenloft, Spelljammer). The only setting that religion is a key aspect of if Theros (befitting it's Greek origin).
To be honest, a deities and demigods book has kinda been a waste. No D&D setting uses Greek or Norse deities. (Well, except Planescape but they use all deities). Aside from a few interlopers to Mystara or Faerun, the vast majority of D&DG are kinda useless. I even question how many DMs use themi in their homebrews rather than make their own.
I at least think most settings can get away with referencing demon lords and archdevils, save for Athas and Eberron at least. Everything existing in the Great Wheel has more or less stopped every setting from having dozens of duplicate lord's of Hell at least.