I have this calc file for about 11 years, every month calculating income and expenses. Recently when I upgraded my version of L.O. into 6.4.0 suddenly I saw almost all dates in a spreadsheet displayed as currency. When before was for example 17/01/2020 now was £43,847.00 or something like this. When I checked cell format in menu it shows correct - date. I was unable to change manually format any of those cells. Either using menu or Ctrl+1.Same problem in L.O 6.3.4. When I returned back to version 6.3.3.2 problem disappeared. All dates displayed back as dates.
What you write looks not like a question to other users (like “How do I do this?”), but as some kind of problem report (“I want to tell you that there’s a problem in new version: …”). This site is not for bug reports: please file this appropriately, and attach a sample document with the problem there.