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