The new season\show tile in the episode row doesn’t navigate seasons so it won’t help with that. It plays the next unplayed episode in that season; which is already automatically highlighted on the screens you see that new tile by default (and there’s multiple other ways to “play next” depending on where you’ve started).
There’s a season navigation bar along the top of the TV details screens on Roku to navigate the seasons. Hit up on the remote to get to it and then you can flip between seasons. To go to the Show level it’s in the overflow menu from any TV detail screen too. To be fair, it’s not super obvious and can be easy to miss until you notice it or use it. I usually just hit “back” instead if I started at a show or season level (like browsing via Library vs Continue Watching).
They added SHOW to that navigation bar now in the New Experience which I think is an improvement over going into the overflow menu so I think that was a good update.
There’s some more detail\convo in the other thread about this new tile.
I’m hoping it’s something for Plex Movies and TV which doesn’t have good navigation and it’s a bug that it showed up on Roku for local media.
Edit: I’m not doing a good job leaving this stuff alone. 
