The new raid consists of 11 bosses, and Anduin appears as the 8th named character. During the first open week of the raid, you will face up to Anduin. This part was intentionally planned and allowed us to take a closer look at Anduin's story before the final showdown. You can learn a lot from this story.
The story of rescuing Anduin takes precedence. By subduing Bolvar and Jaina at once, it was clear that the domination magic used by the guard was very powerful. To deal with the guard, you need to know about this magic. Anduin knows more about the magic of domination handled by the guard than anyone else, so he can work with him to learn how to deal with the magic the guard uses.
Q. You mentioned earlier that in the first week of the raid, you can even face Anduin. After a certain period of time, the next raid area will open, and will it be implemented in a way that will ultimately confront the guard?
Yes. The first week offers an important part of the story, where you can even deal with Anduin and fend off the guard's domination. It was intentionally set for a natural story development. After that, the region will open in time for the opening of Mythic difficulty. Incidentally, the guard is the last boss of the 'burial site of the original being' raid. If the guard is finally defeated, the final curtain of the Shadowlands story will come to an end.