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