Currently, the protocol describes on the documentation is NFS. This protocol is not secure enough for some customers, so they want to use the SFTP protocol instead. To be able to use the SFTP protocol, the package lftp is required, this package needs to be installed by the ReaR installer.
According to our records, this should be resolved by tripleo-ansible-0.5.1-1.20201114030848.2.el8ost. This build is available now.