Here is the full list of all 34 Sekiro: Shadows Die Twice achievements. It takes around 60-80 hours to unlock all of the achievements on Windows.
All achievements have been unlocked.
Defeated all bosses
Attained the "Return" ending
Attained the "Shura" ending
Defeated "Isshin Ashina"
Attained the "Purification" ending
Defeated "Great Shinobi - Owl" at the Hirata Estate
Defeated the "Great Serpent".
Upgraded all Prosthetic Tools to their limit
Defeated the "Great Colored Carp".
Attained the "Immortal Severance" ending
Defeated "Sword Saint Isshin Ashina"
Used Lapis Lazuli to upgrade any tool to its limit
Defeated the "Demon of Hatred"
Acquired all skills
Defeated the "Divine Dragon" and obtained the "Divine Dragon's Tears"
Defeated the "Corrupted Monk"
Traveled to all areas of the game
Defeated "Great Shinobi - Owl"
Acquired all Ninjutsu Techniques
Used the Mortal Blade to sever the Guardian Ape's undying
Upgraded Vitality and Posture to their limit
Acquired all Prosthetic Tools
Defeated the "Guardian Ape"
Caught the Folding Screen Monkeys
Defeated "Genichiro Ashina"
Encountered the Memorial Mob
Defeated "Gyoubu Masataka Oniwa"
Grasped the inner mysteries of any combat style
Defeated "Lady Butterfly"
Fully upgraded the "Healing Gourd"
Returned from the dead using "Resurrection" for the first time
Acquired the Shinobi Prosthetic
Received the "Kusabimaru" from Kuro