Downloads folder shared file write permissions problem - file

Question

I am trying to get an offline backup function working on Android 12. It has worked for years on previous versions of Android, 6 & 8. It is required as the size of the backup can often exceed 25mb. I am using a Samsung A7 Lite for this testing to ensure Android 12 compliance. Essentially the function initially creates a backup folder in the downloads folder if it does not exist. It then writes a backup file to that folder. All goes well. I can repeat the function any number of times without there being a problem. It retains father and grandfather versions for security. However, if I try to use the same function where there are existing files the following day, I am presented with a java.io.FileNotFoundException, open failed EACCES (Permission denied). This whole situation appears very illogical, and does not appear to follow the documentation on accessing the downloads folder. If I manually delete the backup file from the previous day, the process succeeds, similarly if I delete the backup directory within the downloads folder, the backup proceeds successfully. The app asks the user for the appropriate permissions which I believe are read and write external storage. Can anybody identify what I am doing wrong in this environment.
The code is below.
String path = "";
// if no external, set to download
if (path.equals("")) {
File systemPath = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
path = systemPath.getAbsolutePath();
}
// set up backup subdirectory
path = path + "/backup";
// check if path exists
File backupDir = new File(path);
if (!backupDir.exists()) {
try {
backupDir.mkdirs();
MediaScannerConnection.scanFile(this, new String[]{backupDir.getAbsolutePath()}, null, null);
}
catch(Exception e){
e.printStackTrace();
}
}
// first get rid of old backup files leaving at least 2 older versions
File backupFile = new File(path,"backup3.bkp");
if (backupFile.exists())
backupFile.delete();
for (int i = 3;i > 1;i--){
File renameBackupFile = new File(path,"backup" + i + ".bkp");
File existBackupFile = null;
if (i == 2)
existBackupFile = new File(path,"backup.bkp");
else
existBackupFile = new File(path,"backup" + (i - 1) + ".bkp");
if (existBackupFile.exists()) {
try {
existBackupFile.renameTo(renameBackupFile);
} catch (Exception e) {
String message = e.toString();
}
}
}
// create a new backup
String fileName = "backup.bkp";
String backup = path + "/" + fileName;
FileInputStream dataBaseFile = new FileInputStream(DB_PATH);
File newBackupFile = new File(backup);
newBackupFile.createNewFile();
FileOutputStream backupStream = new FileOutputStream(newBackupFile);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = dataBaseFile.read(buffer)) > 0) {
backupStream.write(buffer, 0, length);
}
//Close the streams
backupStream.flush();
backupStream.close();
dataBaseFile.close();
MediaScannerConnection.scanFile(this, new String[]{newBackupFile.getAbsolutePath()}, null, null);