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