I will always be in awe of the folks that figured out all of Elden ring without a guide. Some of those quests were just bananas.
To figure out all of ER, you'd need to play through it multiple times, comb through everything, do things in a different order, etc etc. There was a post on Reddit the other day, someone said they found Jarburg after playing for more than 900 hours. I know of it, but in two playthroughs I don't believe I actually went there yet.
I wonder if they collect analytics and they can at one point say which areas, questlines, gear items, etc are discovered the least.