when I select the game folder, the play button does not appear
It still stays at Setup? Make sure your path doesn't contain any special characters and don't make the path too long either.
HannesC no does not contain special characters and the folder is on the desktop
Move it to somewhere else like C:/Games or so. Reselect the new directory (C:/Games/pluto_t6_full_game) in Setup/Game settings of the launcher.