Story-related, cannot miss.

The ‘End the Tyranny’ achievement is the final story achievement of Hellblade 2, and will unlock after you’ve defeated the final boss and saved the land from the threat of the 3 giants (and more!), which happens at the end of chapter 6.

Do all that and you will just have completed Hellblade 2, and should pretty much have the full 1,000Gs too! Congrats!