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 "Purification" ending
Defeated the "Demon of Hatred"
Defeated "Great Shinobi - Owl" at the Hirata Estate
Attained the "Shura" ending
Defeated "Isshin Ashina"
Acquired all skills
Grasped the inner mysteries of any combat style
Upgraded Vitality and Posture to their limit
Upgraded all Prosthetic Tools to their limit
Used Lapis Lazuli to upgrade any tool to its limit
Attained the "Immortal Severance" ending
Defeated "Sword Saint Isshin Ashina"
Defeated the "Divine Dragon" and obtained the "Divine Dragon's Tears"
Fully upgraded the "Healing Gourd"
Defeated the "Great Colored Carp".
Acquired all Ninjutsu Techniques
Used the Mortal Blade to sever the Guardian Ape's undying
Defeated the "Great Serpent".
Defeated the "Corrupted Monk"
Traveled to all areas of the game
Defeated "Great Shinobi - Owl"
Acquired all Prosthetic Tools
Defeated the "Guardian Ape"
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