https://bugzilla.redhat.com/show_bug.cgi?id=1796271
--- Comment #2 from Jerry James loganjerry@gmail.com --- It looks like the ocaml-cairo build from the mass rebuild, which contains ocaml-cairo-0.6.1, has not yet been tagged into Rawhide. If you see ocaml-cairo-0.4.7-0.28.gitbe5a298.fc32 in your build root, then that is the problem. Hopefully the tagging operation will not take much longer.
In the meantime, if you checkout the ocaml-cairo repo and do a build, then put that build into a repo that mock can pull from, the ocaml-lablgtk3 build should succeed.