How do players find the more intricate secrets in the Dark Souls series?
The Dark Souls franchise has some devilish secrets. Take take just the third installment as an example.
One trophy ("The Usurpation of Fire") requires the player to perform 11 different actions across the entire length of the game in exactly the right order. This often involves talking to seemingly unrelated people or doing things at opposite ends of the game world. Performing actions in the wrong order or performing some other actions invalidates the entire quest. How do people even figure out what they are supposed to do and which exact things need to be avoided to make this possible?
Another example is a secret area (Archdragon Peak) which can be accessed only by performing the correct gesture at exactly the right spot, with no obvious guidance that this is what you need to do.
The series has many more examples, the secret in the bird's nest in DS I being an example that comes to mind.
Are there documented examples of how these kinds of secrets were first discovered by the community?
It's important to remember the scale of the Dark Souls playerbase. It's almost impossible for any one person to figure out all of the game's secrets, but Dark Souls 3 sold three million copies. The series is renowned for its intricate puzzles and secrets and people work together to continually solve them.
You can check sites such as Reddit.com/r/DarkSoulsLore or the many Discord groups who dedicate their time to deciphering cryptic messages in item's flavortexts. It is not necessary for one person to solve everything, but even a fraction of the game's immense player-base has enormous power to piece things together.
With that being said, it's not as if they're going in blind. Many items, spells, and equipment have descriptions which provide hints to some of the more obscure lore of the game. All of which can be used to parse the intricate story the game has created.
You can some read relevant info here
Player community is huge and dedicated. Story telling is deliberately made very vague to encourage players to fill the gaps and discuss their findings and theories. Players not only explore game world, they also try to hack into game files. For example, there are lots of videos describing unreleased content - DS3 unused content on Youtube.
There are a lot of small pieces of information hidden in game - they could be item descriptions, developer messages available only after using special spell (as Seek Guidance is DS3) or even cleverly placed objects: for example, the spot to open portal to Archdragon Peak actually has some corpses sitting in the position very similar to Path of Dragon gesture.
There are not so many NPCs in all games and even less of traditional "quests". So number of possible interaction is limited and some choices are actually obvious - found some eyes? How about bringing them to the only NPC without eyes?