Make sure the network is actually up at the moment of the service startup:
https://systemd.io/NETWORK_ONLINE/

--- galera-26.4.18/garb/files/garb.service	2024-04-17 19:39:35.000000000 +0200
+++ galera-26.4.18/garb/files/garb.service_patched	2024-06-09 07:47:19.245480639 +0200
@@ -4,7 +4,8 @@
 Description=Galera Arbitrator Daemon
 Documentation=man:garbd(8)
 Documentation=https://galeracluster.com/library/documentation/arbitrator.html
-After=network.target
+After=network-online.target
+Wants=network-online.target
 
 [Install]
 WantedBy=multi-user.target