I get the same issue with the apt repository package, its definitely the package. It appears the Opus input plugin is from the Id build, maybe one of the scripts wasn't updated to handle it, or the build of that failed?
ldd won't show it, since its dynamically loading those libraries at runtime, and the input plugins have no other hard dependencies inside that folder.
But this would show it, for example:
strings libin_Opus.so | grep "Media Center"
dev@debbuster64:~/workspace/Development$ strings /usr/lib/jriver/MC28/Plugins/libin_WAV.so | grep "Media Center"
/usr/lib/jriver/Media Center 28
dev@debbuster64:~/workspace/Development$ strings /usr/lib/jriver/MC28/Plugins/libin_Opus.so | grep "Media Center"
/usr/lib/jriver/Media Center Id
I assume it works for you because you actually have an Id build installed as well.