Based on @Tiziano1960 question (and it is a very common doubt when work with media files), I would like to share a way that I have found to share my files (mp3, png, etc…) with third part - I guess that this tip will be useful for both Android and iOS versions.
When you install your app, all the files are saved in a “hide” directory (you see only if you have a root access, I think) and you cannot share them unless you copy those files into a specific folder (common for the majority Android Phone). Fortunately, our collegue (@Taifun) developed an extension that do it in a very simple block (see https://puravidaapps.com/file.php). Remember: “fromFileName”, use “//file.mp3” or “//file.png” and for “toFileName”, use “file:///mnt/extSDcard/file.mp3 or file.png” (warning: some devices has different “common” path - mnt/extSDcard or storage/emulated/0 etc…).
@thunkable team, please fix or add comments if I write something wrong.
I hope that I have collaborated with those who had difficulties on this matter.