In general paints are permeable to water. Most consumer paints will not be up to the job. Certainly standard gloss and eggshell will not last more than a few weeks of regular usage if there is water running down the wall.
There are other ways of lining a shower. If you find out what look you are going for then you might be able to find something suitable.
If you do go down the paint route then I would look at something from the yacht and boat market. Even then I would suggest the plaster behind would give you problems with efflorescence and damp build up. Maybe you use marine ply but then you’d have to think about a more suitable material.
Industrially there are plenty of pain products that would be suitable. I’ve no idea how a consumer would get hold of them though and without correct equipment to apply them and ppe to cover you for their hazardous nature you’d be better off avoiding them.