Answer:
In contrast to the old version, the latest version includes new additions and improvements in the functionality as well as revisions. Therefore, the results of the new version would still not be viewable in the Viewer of the old version.
In general, the functioning of the Dlubal Software program versions is not retrograde. This is only valid for the normal versions for viewers.
The best solution is to install the viewer of the same RFEM version on which the results have been saved.