MariaDB Galera stop working without network connectivity
Galera can't do that, unfortunately, although you can configure it to handle shorter network outages. (See Galera's config tips for WAN replication.) Nodes have to be connected for Galera's global ordering to work so that it can merge writes from multiple nodes. See e.g. here

Maybe what your application could do instead if a node loses network and becomes unavailable (which could be detected by the application or a DB proxy) is to automatically fail over to a different cluster node. However, that still requires network connectivity to this other node.

So if your architecture needs to be tolerant against network losses between nodes, then you may have to look for a different solution.