I have been ALWAYS able to look at and read files from a SD Card using a function cFilePicker that I put up here (my Music Program reads the MP3 files on the SD Card).
I haven't tried any writes. Just reads and copies
Do I only need the external storage access to write?
NOTES: I am using a true Micro SD Card for my tests - Most of my devices are Samsung (if that is a factor)
If they are all Android 4.2 then it works. Starting from Android 6 you need to use Runtimepermissions and starting from Android 10 you´ll get no access to the external storage without using StorageAccessClass.