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.
Defeat Ranrok
Subdue the Lord of the Shore
View all Pensieve memories
Visit Poidsear Coast
Wield a Deathly Hallow
Complete all tiers of a challenge
Learn all spells
Follow butterflies to a treasure
Brew every type of potion
Save a dragon
Upgrade a piece of gear 3 times
Stun 10 different enemies using a Mandrake
Upgrade a piece of gear
Meet Charles Rookwood in the Map Chamber
Spend 5 Talent Points
Find the Map Chamber as a Gryffindor
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 Ravenclaw
Rescue the phoenix
Win the House Cup
Complete Natsai Onai's relationship line
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 collections
Breed every type of beast
Grow every type of plant
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
Defeat enemies in all battle arenas
Complete all Merlin Trials
Discover all cairn dungeons
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
Reach Level 40