The preview buttons / enketo links work a bit differently between published forms and draft forms. I would try re-publishing the draft form with a new version and see if it regenerates the enketo link and starts to work? If you publish an entirely new test form, does the preview link work? (Issues with Enketo links is one of many reason we've been developing Web Forms, which are now available in Central v2025.1.)
The XForm is the XML form and the XLSForm is the spreadsheet form. The names are very similar! It's possible Briefcase only gave you the XForm XML? Can you still get the XLXForm XLSX/spreadsheet files of the forms from the old server? It should be possible to upload the XLSX file as a new draft on an existing form. It will probably complain about conflicting versions (22022022...) but aside from that, I think it should work. Then Central will re-generate the XML from the XLSX file and you'll have both.