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 the "Great Colored Carp".
Defeated the "Great Serpent".
Acquired all Ninjutsu Techniques
Used the Mortal Blade to sever the Guardian Ape's undying
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 "Corrupted Monk"
Traveled to all areas of the game
Defeated "Great Shinobi - Owl"
Defeated the "Guardian Ape"
Acquired all skills
Caught the Folding Screen Monkeys
Fully upgraded the "Healing Gourd"
Upgraded Vitality and Posture to their limit
Grasped the inner mysteries of any combat style
Encountered the Memorial Mob
Defeated "Lady Butterfly"
Defeated "Genichiro Ashina"
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.
Defeated all bosses
Upgraded all Prosthetic Tools to their limit
Acquired all Prosthetic Tools
Attained the "Purification" ending
Attained the "Return" ending
Attained the "Shura" ending
Used Lapis Lazuli to upgrade any tool to its limit
Defeated "Great Shinobi - Owl" at the Hirata Estate
Defeated "Isshin Ashina"