LibreOffice writer -> Menubar -> File -> Reload show an checkbox (when the file isn't empty), but why is it an toggle function that need an checkbox gtk3 and qt5 backend.
Because a document can have a property to be reloaded every x seconds (at least via ODF meta:auto-reload and API css::document::XDocumentProperties::setAutoloadSecs() and setAutoloadURL() and HTML import with "refresh" attribute), which then is indicated by the checkbox. Not a bug.