You have to differ between ostree and rpm-ostree, which are different packages (plus ostree-libs, which is another package).
rpm-ostree is used on Silverblue instead of dnf. rpm-ostree itself depends on ostree. But ostree is also on the normal Fedora release a potential dependency for other packages. It is a flexible tool/lib that can be used for multiple purposes. It is not limited to the rpm-ostree use case.
Do you use flatpak in some way? That depends on the ostree capabilities as well, but of course ostree might be used in other applications, too.