Here is the full list of all 45 Hogwarts Legacy achievements. It takes around 60-80 hours to unlock all of the achievements on Windows.
Complete all collections
Defeat enemies in all battle arenas
Spend all Talent Points
Reach Level 40
Complete all Merlin Trials
Find all Demiguise statues
Win the House Cup
Complete Natsai Onai's relationship line
Complete Sebastian Sallow's relationship line
Complete Poppy Sweeting's relationship line
Defeat Ranrok
Breed every type of beast
Subdue the Lord of the Shore
View all Pensieve memories
Complete all side quests
Discover all cairn dungeons
Unlock all Floo Flames
Upgrade a piece of gear 3 times
Rescue the phoenix
Defeat a total of fifty enemies using Petrificus Totalus
Wield a Deathly Hallow
Reach the highest point in the castle, the Headmaster's upper study
Beat Imelda's time in all broom races
Visit Poidsear Coast
Learn all spells
Save a dragon
Brew every type of potion
Use Flipendo ten times – to tip one cow or several
Upgrade a piece of gear
Reach a combo of 100
Meet Charles Rookwood in the Map Chamber
Stun 10 different enemies using a Mandrake
Grow every type of plant
Complete all tiers of a challenge
Follow butterflies to a treasure
Spend 5 Talent Points
Find the Map Chamber as a Ravenclaw
Invoke Ancient Magic for the first time
Survive the troll attack on Hogsmeade
Attend your first class
Complete the introduction and finish the Sorting Ceremony
Find the Map Chamber as a Slytherin
Find the Map Chamber as a Hufflepuff
Find the Map Chamber as a Gryffindor
Use Ancient Magic on every enemy in the game