Some of the trickier components of this achievement are the achievements for discovering all the named locations on each planet and then in the game as a whole via the planetoids/space stations and some challenge areas. This only needs to be done for the original base game, game updates and DLCs don't apply here but... that may not be the case for some players as this achievement has been known to be very buggy. Another point of contention that makes this achievement harder for some players is the achievement "Tales From the Eridian Slab" not tracking correctly as well as few side quests not showing up for some players. I'll provide details on all the locations, the slabs, and the location of side missions as some links.
https://www.gosunoob.com/borderlands-3/eridian-writings-loca...http://www.powerpyx.com/borderlands-3-all-named-locations-gu...https://gamewith.net/borderlands-3/article/show/11082