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