From Android 5.0 onwards, the location of the external (removable) SD is no longer a fixed path. Instead, the serial number of the SD card is used in the path. For example, on my Samsung Galaxy S4 which is running Android 7.1.1, the physical external removable SD card path is /storage/4975-1401/.
In addition, the root of the external SD card (e.g. /storage/4975-1401/) is now read-only to Android apps. This means if your app needs to write to the SD card, it must do so in the application sandbox directory (e.g. /storage/4975-1401/Android/data/your.app.package.id/files).
cordova-plugin-file does not enable you to access the external (removable) SD card: for example cordova.file.externalRootDirectory returns file:///storage/emulated/0/.