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