Quick answer
Steam lists 25 achievements. Several depend on broad collectible sets, including 61 text logs and 22 audio logs, so completion is easier with chapter tracking.
Official count
The Steam statistics page lists 25 achievements. Platform trophy names or completion percentages may vary, so this page does not copy community rarity values as permanent facts.
Efficient planning
Track text logs, audio logs, and physical collectibles from the beginning. Complete a normal run before committing to the New Game Plus hidden-ending path. Use manual saves where the platform allows them, and verify that an achievement registered before overwriting a late-game checkpoint.
Check the in-game achievement list after each major objective so a missed trigger is noticed before the next long chapter.