As you progress through the story, you'll unlock the Zero Sanctum.
One of the weekly quests requires you to clear the Zero Sanctum mission a certain number of times.
Have you already played all the Zero Sanctum missions available?
That's okay. You can replay missions you've already cleared.
You won't get the first-time clear reward again, but
you can still get embalming upgrade materials and Sanctum enhancement items by replaying the mission.
▲ You can obtain progress and embalming enhancement materials, etc., even from Zero Sanctum missions you have already cleared.
▲ Don't forget to clear the Zero Sanctum bounty requests that take place every week.