If it is planned to use as a fireplace, then you will need to use a stain block paint to stop the soot, followed by heat resistant paint. I forget what the stainblock is called here. it’s hideously expensive but works a treat…a workman forgot to put the top on the oil tank on his compressor and sprayed mucky oil all over one of our new walls. So no matter how much we washed it we could still see the stains. One coat of stain block and as good as new.
If you are thinking of tiles then again be careful about heat, as some tiles won’t resist high temperatures. We put a new stove in one room, and lined the wall behind with the stones tiles we used on the floor (and before someone protests the wall was already insulated with fireproof insulation). You can also use porcelain tiles made for fireplaces.