We have documentation for Installing  Percona XtraDB Cluster in multi-namespace (cluster-wide) mode, but not for the upgrade.

Install doc: https://docs.percona.com/percona-operator-for-mysql/pxc/cluster-wide.html

need upgrade doc as well for the same setup

Example:

Created Percona XtraDB Cluster in multi-namespace (cluster-wide) mode with pxc and pxc-operator namespaces as described in documentation Here

Upgrade (cluster-wide) mode pxc-operator

Upgrade test example: