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