Why does my LibreOffice Writer export filetype default to jpg?

When I download a .doc file from the internet into LibreOffice, it is loaded into Writer, as expected; but when I want to export it, the export filetype always comes up as .jpg, which is really non-intuitive, and requires me to take extra steps when exporting. I have looked at the LibreOffice documentation, but I don’t see any way to override this “feature”.

How can I tell LibreOffice Writer that I want to export to a particular filetype, e.g. html, by default?

What do you mean by ‘export’, do you use File → Export, or File → Save as?