Hello,
I don't know the solution, but maybe my thoughts will help.
By default, the home folders such as downloads, documents, ... are created on all storage devices. With the photo app you can decide whether you want to save it to the internal memory or to the SD card. As far as I know, that doesn't need manual symlinking.
Which file system does the SD card have?
Could it be a rights issue with vfat?
Many greetings, Charly