Qt 6 makes DataStream saved with Qt 5 not loadable if using QList<...>

Saving to DataStream containing a QList<anything> from Qt 5 will make the file not loadable with Qt 6. We're switch our app to Qt 6. It means all users won't be able to load their file because we serialized a QList in it. I couldn't find how to handle that.

I attached a sample file that, when compiled with Qt 5 will save a file containing a QList<QString> and when compiled with Qt 6 will try to parse this file and fail (in our app  that's a QList of a custom type of course).

It might not be necessary to fix it in Qt, but we need a solution to reload file saved with previous software releases.