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