The last chapter is a short walk with no enemies and one pickup, so take the comic before you go on along the path. Long scenes play before you get control.
Walk to the fenceHidden spoiler – activate to revealQuest stepMinor spoiler
Location
Jackson · Epilogue – When you get control, leave the road for the woods and climb through the barbed-wire fence.
Comic: SingularityHidden spoiler – activate to revealCollectibleMinor spoiler
Location
Jackson · Epilogue – Past the fence, go right through the trees to the broken-down truck by the rock face, with the comic on its driver's seat. Turn it over when you read it.
Ending and creditsHidden spoiler – activate to revealEndingMinor spoiler
Location
Jackson · Epilogue – Walk on along the path until the final scene starts, then let the credits roll. The game has one ending, so there's nothing to choose.
Finishing the story writes a Story Complete autosave. Keep it, or make a manual save, before you replay anything: loading a chapter locks every later chapter on that save, and reloading the Story Complete save brings them back with your collectibles still counted. Left Behind comes next, from its own entry on the main menu. After that, Chapter Select clears anything its menu shows as short. It doesn't show Tools, and a Tool taken on a replay may not count. A shiv door needs a shiv, and a replay may not bring your supplies, so check before you start.