Reddit:
So to solve the problem, go into desktop mode and open Steam. Open Steam > Settings > Downloads and click the Steam Library Folders button under Content Libraries. Select the rogue External Drive entry, click the three dots to the right of the storage meter and choose Remove Drive. Once that's done, click the little plus next to the list of drives, select /run/media/mmcblk0p1 and click the Select button.

Зайди в Desktop режим, в настройках "стим папок" убери карточку, выбери "добавить новую" и "задать путь вручную". /run/media/mmcblk0p1. Если не поможет, то хз