There is no Culture rules container in any way, and Backgrounds are not cultures.
D&D backgrounds are "learned", and by definition, are cultural in nature.
The 2024 rules, and the shallow extent that any kind of guidance is provided, does nothing from what I can see to aid or teach, world building at all.
If you want deep dives into setting lore, then purchase the coming soon Forgotten Realms guides. Or even use the Forgotten Realms guides from earlier editions. No problem!
Or purchase Eberron. Or Theros. Or Dragonlance. Or whatever flavor you enjoy most.
I myself am literally implementing setting content from Original D&D, 1e, 2e, 3e, even 4e, for my Blackmoor regional setting.
Heh, as you might know, I hate Forgotten Realms gods any way. It is impossible for me to take them seriously, and difficult for me to understand how people could "worship" them.
I like Eberron with its religious relativity and cultural focus. Even Theros is surprisingly excellent, despite its "D&D gods".
Whichever gods you like best, use those for your setting.
I will be emphasizing animism for the subarctic and arctic. But polytheism and monotheism also exist in the Greyhawk planet. Likewise philosophical elementalism is also a thing, which I will lift from Dark Sun.
What of their faiths? Are there actual cultural differences outlined, and how are those mechanically represented if every culture has the same Charlatan, Farmer, and Hermit.
Create backgrounds that make sense to you.
I will have backgrounds that do very specific things. For example, I want "dark elves" to be a culture that includes D&D elves and dwarves, even a human or a gnome. (Gnomes are anachronistic. Nonexistent in the viking period but popular in modern folkbelief. The background feat will grant spellcasting and so on, to cover the salient dark elf tropes.
Those are your Backgrounds. Capital B. That is a Rules Container.
Yes. These are backgrounds that "I make my own"! At the same time, I expect the upcoming Forgotten Realms setting to add official backgrounds that do cool stuff, like allow Avariel elves to make "glassteel", and Drow elves to make "adamantine" weapons and armor.
Tell me, as a 'I just got my first D&D Book, 2024 PHB' who is Gruumsh, and what does he believe and ask of his followers?
I dont care about Gruumsh. I am still trying to decide what the Orc culture should be for my setting.
The themes I find interesting are: Roman underworld (Shadowfell) = "Orcus" = Ogre = Orc. Potentially there is necromantic flavor for the Orc, and Giant flavor.
These tropes are fun, but pejoratively negative. They will definitely be "factions" that can offer "backgrounds". But I need to think thru how to do this in a positive way, that, sotospeak, a reallife Orc would enjoy to play.
Go to your Index. You'll find 'background' on page 378, first page of the index.
You will not find culture. Its not a thing, you are making it up as you have before.
Backgrounds are so easy to create!
Pick whatever skills, tool(s), (languages), that make the most sense
to you. Then pick whatever feat
you feel is appropriate. Pick one of the 2024 feats that you like. Or if you are uncertain about inventing your own feats, then most of the time, you pick one of the 2014 half feats, plus Xanathars and Tashas. All of this is playable at level ! Character concept in play from the moment adventure starts.