Here is the full list of all 42 ELDEN RING achievements. It takes around 80-100 hours to unlock all of the achievements on Windows.
Obtained all achievements
Achieved the "Age of the Stars" ending
Acquired all legendary sorceries and incantations
Acquired all legendary ashen remains
Defeated Dragonlord Placidusax
Defeated Shardbearer Malenia
Acquired all legendary talismans
Defeated Shardbearer Mohg
Acquired all legendary armaments
Achieved the "Elden Lord" ending
Achieved the "Lord of Frenzied Flame" ending
Defeated Hoarah Loux the Warrior
Defeated Maliketh the Black Blade
Upgraded any armament to its highest stage
Defeated Godskin Duo
Used kindling to set the Erdtree aflame
Defeated Fire Giant
Defeated Elemer of the Briar
Defeated Loretta, Knight of the Haligtree
Defeated Commander Niall
Defeated Mohg, the Omen
Defeated Shardbearer Morgott
Defeated Dragonkin Soldier of Nokstella
Defeated Godfrey the First Lord
Defeated Magma Wyrm Makar
Defeated Lichdragon Fortissax
Defeated Shardbearer Rykard
Defeated Godskin Noble
Defeated Astel, Naturalborn of the Void
Defeated Valiant Gargoyle
Defeated Regal Ancestor Spirit
Defeated Mimic Tear
Defeated Shardbearer Radahn
Defeated Royal Knight Loretta
Defeated the Leonine Misbegotten
Defeated Ancestor Spirit
Defeated Rennala, Queen of the Full Moon
Defeated the Red Wolf of Radagon
Restored the power of a Great Rune
Defeated Shardbearer Godrick
Defeated Margit, the Fell Omen
Arrived at Roundtable Hold