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