When I checked the RPG section, only two of the Paper Mario games were listed. The first Paper Mario and Thousand-Year Door. Which is appropriate from what I see, since the former is like a story that has its origins as a Super Mario RPG follow-up (Mario Story) and the latter is explicitly an RPG (it's called Paper Mario RPG in Japan). If you are wondering, the Paper Mario games after Thousand-Year Door are listed under "Adventure" (all four of them, including Origami King). I used to think that Thousand-Year Door is the transition point for Paper Mario to have a bigger focus on the creative uses of paper, but I suppose Super Paper Mario has a hand in it for focusing away from the traditional RPG aspects.
Paper Mario has been added to the Japanese Mario Portal
In general, games that act as transitions between the old approach and the new approach is fascinating, because in a lot of cases they are lauded as the best games, such as Pokemon Black/White. For example, the name is a call back to the simple colour names of older games, but it has a double meaning on the game's story, which future versions will use to their advantage, including Sun/Moon and Sword/Shield. Those games also have some things that are the last in line and the first in line, such as the use of sprites for the former and streamlining the adventure into a linear path for the latter.
Thank you for reading.