Looking at the mirror list for an archived version, e.g. https://mirrors.rockylinux.org/mirrorlist?arch=x86_64&repo=vault-AppStream-8.5
shows:
# repo = vault-AppStream-8.5 arch = x86_64 country = US country = global
https://dl.rockylinux.org/vault/rocky/rocky/8.5/AppStream/x86_64/os/
But this URL doesn’t work: https://dl.rockylinux.org/vault/rocky/rocky/8.5/AppStream/x86_64/os/
It should be: https://dl.rockylinux.org/vault/rocky/8.5/AppStream/x86_64/os/ (i.e. with one less rocky/
)