Slanted wall - How to best straighten it?

Hello everyone,

I have a load-bearing wall made of pumice stones in the future bathroom, which slopes at the end (red line in the attached sketch). The shower will later be placed in the corner, and tiles will be applied to the wall. Now I would rather not keep this slope. How can I best get rid of this slope?
Build up with solid blocks or simply put drywall in front of it?
Do you have any tips on what can be done?

Just hide it behind the drywall.

Well, I would very much prefer not to put another stud wall in front of the slanted wall. That would lose even more space...

You can also install the drywall board without a stud frame using setting plaster, or simply plaster it thickly in several layers.

Can't this also be made to look different with different colors? I mean some kind of optical illusion?