Samsung
Mount SD Card Manually in Storage Settings auf Samsung
When a Samsung phone lists an SD card under Battery and device care but apps still cant read it, the card is usually inserted but not mounted. Mounting tells the system to make the card's file system available for read and write access. Without this step, the card sits idle even though the hardware slot detects it correctly.
This mismatch happens most often after a restart, after removing and reinserting the card, or when the card was formatted on a different device. One UI sometimes skips the automatic mount step if it cannot verify the file system right away, especially on One UI 3 and earlier builds.
Mount the SD card manually
Open Tap on Settings ➔ Tap on Battery and device care ➔ Tap on Storage ➔ Open the Menu ➔ Tap on Advanced ➔ Tap on SD card ➔ Tap on Mount. The card becomes available within a few seconds and shows up again in the gallery, camera settings, and file manager.
If the Mount option is missing or greyed out, the card itself may be damaged or use an unsupported file system. In that case, try the card in a computer first to rule out a hardware fault before repeating these steps.
Unmounting before removing the card protects it from write errors. Mounting again after every reinsertion is expected behavior, not a sign of a faulty card.