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