Here is the full list of all 31 Stranger Things 3: The Game achievements.
Beat the game on New Game+
Complete the game
Complete Mall Showdown
Found all 50 hidden gnomes.
Complete Cabin Ambush
Complete 30 Minutes or Less
Complete Invasion of Privacy
Unlock Steve
Unlock Erica
Complete Wall Flower
Complete Hospital Brawl
Found 25 hidden gnomes. Half-way there!
Craft 5 trinkets
Unlock Will
Complete Ivan the Smuggler
Complete Store Raid
Unlock Hopper and Joyce
Unlock Eleven
Complete Chores for Granny Perkins
Successfully hack the hardest level chest/door
Unlock Max
Unlock Jonathan
Unlock Nancy
Complete Rats in the Walls
Complete On the Wire
Complete Break In, Make Out
Complete Revenge of the Geeks
Complete Radar Love
Crafted your first item
Unlock Dustin
Complete Sneak Peek