Here is the full list of all 58 Final Fantasy IV (3D Remake) achievements. It takes around 80-100 hours to unlock all of the achievements on Windows.
You earned all achievements.
You finished the game on Hard difficulty.
You defeated Proto-Babil.
You completed the entire Bestiary.
You obtained all the Onion items.
You defeated Geryon.
You obtained Adamant Armor.
You acquired all hidden summons.
You finished the game twice.
You defeated 2,000 enemies.
You obtained all augments.
You finished the game.
You raised Cecil (Paladin) to level 70.
You played through all Namingway events.
You obtained Ragnarok, Holy Lance, Murasame, and Ribbon.
You traveled across the entire map.
You earned 500,000 gil.
You obtained Excalibur.
You defeated the CPU.
You defeated the elemental archfiends.
You acquired all summons.
You earned 200,000 gil.
You went to the moon on The Lunar Whale.
You defeated Demon Wall.
You raised Cecil (Paladin) to level 50.
You defeated 1,000 enemies.
You completed 60% of the Bestiary.
You obtained 20 augments.
You defeated Rubicante.
You defeated Dr. Lugae.
You talked to everybody in the Developers' Office.
You defeated Calcabrina.
You defeated Barbariccia.
You raised Cecil (Paladin) to level 30.
You defeated the Magus Sisters.
You earned 50,000 gil.
You defeated Dark Elf.
You completed 30% of the Bestiary.
You raised Cecil (Paladin) to level 20.
You defeated Cagnazzo.
You raised Cecil (Paladin) to level 10.
You defeated Scarmiglione.
You defeated 500 enemies.
You raised Cecil (Dark Knight) to level 25.
You earned 10,000 gil.
You were shipwrecked by Leviathan.
You defeated Mom Bomb.
You defeated the Sahagin that attacked at Kaipo.
You raised Cecil (Dark Knight) to level 20.
You traveled to Damcyan Castle.
You completed 10% of the Bestiary.
You raised Cecil (Dark Knight) to level 15.
You defeated 100 enemies.
You obtained one augment.
You acquired one summon.
You traveled to Mist.
You talked to everybody in the Training Classroom.
You played a new game.