Simple .spec file change may be to strip "@localstatedir@" from the service file during the %prep stage. https://sourceforge.net/p/opendkim/git/ci/master/tree/contrib/systemd/opendkim.service.in Reporting against rawhide since I don't see anything handling this in https://src.fedoraproject.org/rpms/opendkim/tree/master
This bug appears to have been reported against 'rawhide' during the Fedora 34 development cycle. Changing version to 34.
Fixed in 2.11.0-0.19, building for el8 and f35 F35: https://koji.fedoraproject.org/koji/buildinfo?buildID=1717015 EL8: https://koji.fedoraproject.org/koji/buildinfo?buildID=1717016
Closing for current release Fedora 35.