Your question is unclear..could you add more detail what you are trying to achieve?

I want beadboard/trim like this and a mirror added to my small bathroom and not sure how to do it .

I think his goal is to attach the mirror parallel to the wall which he could accomplish by (a) cutting the wainscotting and trim to the shape of the lower portion of the mirror and attaching the mirror to the exposed drywall, or (b) cutting a piece of, say, wood the shape of the upper portion of the mirror and thickness of the trim, attaching that piece of wood to the wall, and then attaching the mirror to the piece of wood. I would only do the latter.

In the photo it appears that the person hanging the mirror just cut a rectangular piece of wood, attached the wood to the wall, and attached the mirror to that piece of wood. That's why you can see the gap between the mirror and wall.

The bead-board does not have to be that tall.. the trim can be flatter…or the mirror can be a little shorter…if you are building this you can accommodate your needs with little variations such as these… in fact in this picture the cabinet and bead-board look taller than necessary?

Looks like something was secured on the wall first so the mirror hangars would bring mirror out from the wall.

A block of wood would be attached to the mirror or to the wall to bring the mirror forward.

Maybe get a round mirror like we did here so the mirror doesn't overlap the beadboard:

Beauty and the Baths: Jewel Box Powder Room · More Info

Short-person perspective here... If the mirror gets moved higher than the bead board I won't get a good view of myself. If you are all tall that's not an issue. I think you have a decent solution with the blocking attached to the wall at the top to make the mirror vertical.

I have done this before by putting a small 2x4 on the wall and hanging the mirror on the 2x4. Make sure you attach the 2x4 to the studs.

I used a pivoting mirror for a similar situation. The pivot points hold it out from the wall and it doesn't look like a mistake.

(Bonus--short people can use it too!)

@Fori that's right! There is a pivoting mirror at work. Not sure why. I also don't know why someone tipped it to angle down. It makes everyone look short. I recy tipped it so it's perpendicular to the ground and like it more.

Pivot mirror example. I had one installed in a bathroom we remodeled. Handy for both tall and not-so-tall users.

I think they make hooks/hanging hardare that hang things slightly away from the wall at the top for situations like this.

(Of course I hope people in my house don't ACTUALLY mess with the mirror angle. I did install it myself after all. 😁)

Pivot mirror is a great solution!