When connected through USB, your SD card may not be detected by your PC for a number of reasons:
Your SD card can be defective or damaged, which would make it impossible for your PC to recognize it. Check a different SD card to determine if the issue still exists.
Connection problems: Verify that the USB cord is functioning properly and that your phone and PC are properly connected. To see if the issue is fixed, try an alternative USB cable.
Driver problems: The SD card may not be identified if your PC does not have the required drivers installed for it to recognize your phone. Attempt to obtain and install the most recent drivers for your phone from the maker's website.
Incorrect settings: Check the settings on your phone to ensure that it is set to transfer files and that the SD card is not being used as internal storage.
Outdated software: Make sure that both your phone and PC have the latest software updates installed, as outdated software can cause compatibility issues.
If none of the above solutions work, it may be helpful to consult with a professional or contact the manufacturer for further assistance.