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