Why is My SD Card Not Detected by Any Device?

In my opinion, the easiest solution that you can apply is to check the connection between your SD card and the phone/PC. Either grab a soft cotton to clean the SD card or try a new SD card reader to reconnect the memory card and device, then head to see if it can be detected. 

On top of that, you can also update the phone driver and computer driver to make the SD card be detected. Let me show you how to perform:

Update the phone driver

Step 1: Connect your phone to your PC.

Step 2: Go to Control Panel > System > Device Manager.

Step 3: Locate and expand Portable Devices or Other Devices, depending on which one you see.

Step 4: Right-click the name of the device you connected, and then select Update Driver Software.   

Update the computer driver

Step 1: In the search box on the taskbar, enter device manager, then select Device Manager.

Step 2: Select a category to see the names of devices, then right-click (or press and hold) the one you'd like to update.

Step 3: Select Search automatically for updated driver software.

Step 4: Select Update Driver.

With these updates being performed, you can check if your SD card is detected. If not, then I can determine that your SD card is failing. For your storage demands, buying a new SD card is recommended.

Hope this answer can help you!