Help setting up Galera Arbitrator
Two node galera is a fundamentally broken design as it cannot maintain uptime without a quorum and the ability of a node to go down to aid recovery.
garb is a toy test thing and not a production tool.
Use 3 nodes all as full galera member nodes.
Use haproxy in a redundant configuration on all nodes. Use a different IP addresses for haproxy and galera without overlap.
If it can't be reliable in test then it won't be reliable in production.