What’s the best way to find the version number of the latest starred version

"whoops, that didn't go through..." is the default blanket error message that CommCare HQ will generate when something went wrong and it wasn't able to tell you what. Generally in this situation the best option is to "report an issue" so that the platform developers can figure out what's going on and introduce a better error message for future occurrences of the problem.

If you are blocked, I would recommend using the "revert" feature to go back to a previous working version of the application, recognizing that this will cause some of your recent work to be lost.

Without rooting the device I'm not sure of a good way of making any folder read only.

One option could be to place a .nomedia file in the folder where the multimedia is located. This will prevent Android from scanning the folder for media and hence it won't show up in any albums etc.