In one of my applications I need to open files that are stored as blobs in a database. Therefore I save them in the path I get from QStandardPaths::writableLocation(QStandardPaths::TempLocation).
If I read the doc of QStandardPaths::writableLocation(StandardLocation type) correctly, this returns me a QString with the path of writable the StandardLocation or empty string.

But when I try to write a file to this location I get a "Permission Denied" Error on some Windows machines. even though I can create a file there when I open the location with the file browser and do right click -> new file
(On other windows and linux machines there is no problem to write the file into the TempLocation and open it with QDesktopServices)

        q.prepare("select * from attachments where ID=:id");
        q.bindValue(":id",attid);
        q.exec();
        q.first(); //the query is always valid and returns exact 1 row
        QByteArray fc;
        QString fn;
        
            fc = q.value("content").toByteArray();
            fn = q.value("name").toString();

        
        QFile f;

        f.setFileName(QStandardPaths::writableLocation(QStandardPaths::TempLocation) + "/"+fn);
       
        qDebug() << f.errorString();
        if(f.open(QFile::WriteOnly)) {
            f.write(fc);
            qDebug() << f.errorString();
            f.close();

            bool localOpenUrl = QDesktopServices::openUrl(QUrl::fromLocalFile(f.fileName()));
            if(!localOpenUrl)
                QMessageBox::warning(this,"Error","Failed to open attachment " + fn + "\n" + f.errorString());
        }
        else {
            QMessageBox::warning(this,"Error","Failed to open " + f.fileName() + "\n" + f.errorString());
        }

Any ideas or hints what could went wrong (or what I did wrong here) here? (Or any other ways how to open a binary blob from database with the per default program?)