Material selection, leveling a kitchen wall

[Höghus]

I have a kitchen wall that has been a bit crooked.
The left side is chipboard, the right side is chimney breast. The wood stove and electric stove followed the line from the chimney breast, the countertop followed the line from the chipboard, resulting in a skewed gap between the electric stove and the countertop, the opening in the back. The plan now is to take down the chipboard, attach furring strips to the studs on the right side, and put the board back. Then fill in with "something" on the chimney breast so it's even with the chipboard using a 6mm gypsum board. After that, tile over the gypsum and chimney breast.
The question is what should I use as "something"?
So what should I use to fill in on the chimney breast?

/Höghus

 

[Höghus]

Would gypsum plaster work?
It seems that the drying time for rendering is significantly longer.

/Höghus

 

[Höghus]

There is 1-2cm of plaster already on the bricks the chimney is built with. Some small cracks in the plaster around the flue pipe.

/High-rise building

 

[Höghus]

Consulted the chimney sweep who thought gypsum plaster was excellent.

/Höghus