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