Thanks for trying this out @churchyard. This software is still in an early state, and only supports the clone, sources, and new-sources commands so far. This is documented in the upstream readme. Of course in the future we plan to get mockbuild and build commands working.
This update bumps the soname from libfmt.so.3 to libfmt.so.6. This is a breaking change which is against EPEL Policy. mkvtoolnix no longer installs and needs to be rebuilt against the new soname. Why wasn't the Incompatible Upgrades Policy followed?