borgmatic 1.3.15 is released. Simply updating borgmatic would perhaps solve the dependency error blocking installation, since the pinning to an older version was resolved in an issue and recent release: https://projects.torsion.org/witten/borgmatic/issues/203
For now, the simplest method seems to be to just install directly with: sudo pip3 install --user --upgrade borgmatic as per the documentation, notwithstanding standard warnings against using pip/pip3 as root.
borgmatic is now un-borked. The package in the repo has been updated after a new maintainer took over.
borgmatic tends to have many rapid releases, which take time to get accepted into the main Fedora repo. For quicker access to the latest packages, there is the new maintainer’s copr: heffer/borgmatic Copr