Once you have completed the story for the first time on any difficulty you will unlock the Extra Content Shop.
You can access this shop through the main menu under Bonuses. Concept art is purchased through this shop.
The Extra Content Shop uses a type of currency called CP (Completion Points). CP is earned by completing challenges throughout the game (many of these challenges are the requirements of achievements).
A list of all the challenges and the CP rewarded for their completion can be found under the Challenges menu under Bonuses or can be found here: https://residentevil.fandom.com/wiki/Challenges
There is a total of 120 concept arts that are required to be purchased for a total of 12,000 CP. You are awarded 1,000 CP for purchasing all 120 so you will lose 11,000 CP total.After purchasing all 120, you need to go into the Concept Art menu and scroll through all of them so that the red notification is removed in order to unlock the achievement.
Viewing each individually is not required.