Why can I not export a file?

I just replaced my iMac (system was older version) with a new Mac, Catalina system. I am using LibreOffice I just tried to save a file with the “Save as …” command, and no save window came up. I then tried to export the file with the same result.
Please let me know how to get the file in some format that a person without LibreOffice can use it.

Thank you.

Did you look at the answers to Catalina?