coverin plastic tile wall with panelin or thin plywood. how to cover the seams?
This scenario would come under, "horrendous homeowner repair solutions".
It would never work and in 6 months you'd be covering this up with something else.
Remove the tiles. In my experience, they come off pretty easily. If not, it will require more effort. The rough textured wall, as long as it's fairly flat, will take the next layer. Scrape off the high points if you have them. Go over the wall with 1/4" sheetrock. Tape and compound. If you use adhesive, check to see it's compatible with the plastic adhesive residue.