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