Here is the full list of all 35 A Plague Tale: Requiem achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Open all the secret chests
Interact with all the old protector’s items in the sanctuary
Shoot all the pine cones
Fully upgrade the gear
Fully upgrade the alchemy
Fully upgrade the sling
Recall all souvenirs
Fully improve the Opportunism skills
Find all feathers
Fully improve the Prudence skills
Fully improve the Aggressive skills
Don't kill the guard on the docks
Fully upgrade the instruments
Find all flowers
Extinguish 40 fires
Complete all chapters
Complete chapter 16
Complete chapter 15
Complete chapter 14
Complete chapter 13
Complete chapter 12
Complete chapter 11
Fully upgrade the crossbow
Complete chapter 10
Complete chapter 9
Complete chapter 8
Successfully complete all throws in the Crowns game
Complete chapter 7
Craft 100 ammunitions
Complete chapter 6
Complete chapter 5
Complete chapter 4
Complete chapter 3
Complete chapter 2
Complete chapter 1