EPEL branch uses the same spec file of master branch.
There, it has recently been introduced the new cmake macros [1]

%cmake_kf5
%cmake_build
%cmake_install

but they do not work on EL8 at the moment, so we need to add proper macros to skip them.
You can take as example my spec file
https://src.fedoraproject.org/rpms/darktable/blob/master/f/darktable.spec

[1]: https://fedoraproject.org/wiki/Changes/CMake_to_do_out-of-source_builds