Most of the themes are not designed for a portrait mode - but you can try some of the 4:3 and CRT designed themes. I remember one them ( crt-centered ) had a simpler layout, with video on top of the gamelist, which would maybe fit the bill.

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EDIT: you can run the theme-gallery from the Configuration/Tools->Emulationstation to get previews for different themes, just to see how they fit on your screen.

It was solved by updating all installed packages from the Retropie setup tool.