Galera backup failing with error "mysqldump: Error 1213: Deadlock found when trying to get lock; try restarting transaction when dumping table"
Option 1

Use a replication slave off the galera cluster exclusively for creating backups. You can stop slave to ensure that all DDL operations have finished before doing a dump. Parallel dumping operations like mydumper are also possible.

Don't forget to enable log-slave-updates on the galera member you use as a master.

Option 2

Desync a galera node before doing a backup from it.