Which the DMG should advise the DMWork it out with the player.
YeahGods and pantheons are far beyond what newbie DMs should be doing. Not to mention the possibility of offence if you happen to parody a player's real world beliefs
But they do it anyway
So advise New DM how to do it or warn them of what not to do.
What weapon will the dwarf guards carry and dwarf blacksmith make?These a matters for individuals, not societies.
Which people would be most invested in slaying the undead?
Which people would know where a druid who can cast the spell you need is?
There is an undercurrent of attitude against teaching DMs to move from published setting to their own setting. I suspect it is from fans not wanting practices written down and used against them because "I don't what I'm doing".
But I find from looking at young DMs I mentored that there are common errors and overlookings in world building and campaign framing that no one talks about because the experienced DMs assume everyone knows.
Yet there is a whole sub industry of podcasts and YouTube videos giving out this very info because many people never learn these things and aren't taught or advised about it