Here is the full list of all 25 Untitled Goose Game achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Finish the game
Complete the pub to-do list
Collect the five flowers
Perform at the pub wearing a ribbon
Sail the toy boat under a bridge
Dress up the bust with things from outside the back gardens
Steal the old man's woolen hat
Get thrown over the fence
Complete the garden to-do list
Complete the high street to-do list
Complete the back gardens to-do list
Cabbage picnic
Trip the boy in the puddle
Make the shop scales go ding
Open an umbrella inside the TV shop
Make someone from outside the high street buy back their own stuff
Trap the boy in the garage
Catch an object as it's thrown over the fence
Score a goal
Lock the groundskeeper out of the garden
Earn every other trophy
Complete the garden to-do list before the church bells ring
Complete the high street to-do list before the church bells ring
Complete the back gardens to-do list before the church bells ring
Complete the pub to-do list before the church bells ring