The ARG was made up of Ikora's shredded documents and messages that expand on some of the information in the collector's book e.g. the nature of light & dark, who we can trust and more stuff on stasis. but the biggest boom self is at the page 21 to 30 which expands on what we know about truth to power with a heavy focus on what it was trying to do. it turns out that truth to power might be about Savathûn trying to get into a higher plane of exitances (separate from the ascendant plane/realm) and just like everything else with Savathûn it just brings up more question then answers.

link to ARG https://tjl.co/wqarg/wqarg-v2.pdf Eddit: turns out the the higher plane of existence is IRL