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