Cannot perform Supercluster rolling upgrade to 21.5.30 from versions earlier than 21.5.20 (E-91847)
Due to a software change in 21.5.20, you can only do a rolling upgrade when the installed and upgrade versions are both either before 21.5.20 or after it. For example, you can do a rolling upgrade from 21.5.20 or 21.5.21 to 21.5.30, but not from 21.5.10 to 21.5.30.