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.
Attained the "Return" ending
Upgraded all Prosthetic Tools to their limit
Acquired all skills
Attained the "Shura" ending
Defeated all bosses
Defeated "Isshin Ashina"
Used Lapis Lazuli to upgrade any tool to its limit
Attained the "Purification" ending
Upgraded Vitality and Posture to their limit
Defeated the "Great Colored Carp".
Defeated "Great Shinobi - Owl" at the Hirata Estate
Defeated the "Great Serpent".
Fully upgraded the "Healing Gourd"
Acquired all Prosthetic Tools
Defeated the "Demon of Hatred"
Attained the "Immortal Severance" ending
Defeated "Sword Saint Isshin Ashina"
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
Defeated the "Guardian Ape"
Grasped the inner mysteries of any combat style
Caught the Folding Screen Monkeys
Defeated "Genichiro Ashina"
Defeated "Lady Butterfly"
Encountered the Memorial Mob
Defeated "Gyoubu Masataka Oniwa"
Returned from the dead using "Resurrection" for the first time
Acquired the Shinobi Prosthetic
Received the "Kusabimaru" from Kuro