Is there a repo for the rpm’s posted on the download site that I can hook into dnf?
There is no official rpm (nor deb) repository, you need to ask the maintainers of your distro if there is some extra repository for LibO “fresh” versions. I know openSUSE have one (even if it’s still on 5.4 right now) and ubuntu has a ppa, but I don’t know about Fedora or other distros.