Before attempting to create a file path to the SD card in an Android application, your Java code must first check that an SD card is mounted on the device, as this is not always the case.

Cx File Explorer is a good, basic file browser. It features a relatively modern UI, all of the basics, and support for many cloud storage services and shared storage servers (FTP, SMB, etc).

The Android File Transfer site states that the app supports macOS 10.7 and higher, so you’ll need to be at least on that version if you want to use the software.