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