JabRef has not "Import..." in the Welcome Tab:

It should be easy to migrate from Citavi.

1. Add "Import from Citavi..." to the Welcome Tab
2. A file picker for "Citva XML" should open
3. The content should be imported into a new tab
4. The citation key from Citavi has to be kept

Step 4 means: following preference should be ignored:

I think, in the implementation, a new CitationKeyPatternPrefrence object based on the old one has to be created. Check if the class is already updated following the step at #14400 to enable basing from an existing configuration. If not, do this first.

This is the next step to #14657