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