If a mariabackup or xtrabackup-v2 SST is done with an IPv6 address, then you need to add the pf=ip6 option to socat. This is done by adding the following to the [sst] option group in an option file:

[sst]

sockopt=",pf=ip6"

For example, see the following configuration file from an automated test:

https://github.com/MariaDB/server/blob/4aea6b3e3f3fd1a8a2526bc40fc5e85e571d8242/mysql-test/suite/galera_3nodes/t/galera_ipv6_mariabackup.cnf#L29

Would it be possible for the mariabackup/xtrabackup-v2 SST scripts to auto-detect IPv6 addresses, and then automatically add this socat option, so that users do not need to explicitly provide it?