file://-Uris are not allowed anylonger on higher Android.
You´ll not have access to the folder File.DirRootExternal on Higher androids too.
Do you plan to upload the app to playstore? If so then you have to use targetsdk 30 and also you have to match the requirements.
There are several versioned components that affect the compilation process and the runtime behavior of our apps. The purpose of this tutorial is to explain the differences between them and help you choose which version to use. Each Android version is mapped to an api level. You can see this...
Check especially Runtimepermissions, FileProvider
B4A + B4i example: https://www.b4x.com/android/forum/threads/b4x-texteditor-save-and-load-external-files.132731/#post-838166 List of classes or libraries that can be used to access secondary storages: ContentChooser (Phone libray) - allows the user to select a resource or file using external...
Check Contentresolver to get any file the user have to select.