Here is the solution:
See also in the Taifun File extension description
https://puravidaapps.com/file.php:
Since you don’t have permission to READ from external storage, the (not shown) error is:
java.lang.NullPointerException: Attempt to get lenght of null array at com.puravidaapps.TaifunFile.getList(TaifunFile.java.xxx)
But this error message is not displayed because the app crashes immediately.
So, ask for READ permission before:
Correction, it is.