Yes, I finally found the manpage here https://www.mankier.com/5/rpm-ostreed.conf
However, I just wondered why in this distro the manpage is missing.
Or I may just have not searched right.
Fedora IoT has lineage with the old Fedora Atomic Host distribution and we chose not to include man pages in the OS to save on space, etc. The assumption was that users could login, create a container, install man pages, and get the docs they need.
The the primary use case for these variants was not for regular user access, but rather systems that should “just work” (including auto-updates).