I’m sure this is the oracle dependency but there is breaking change there, and it looks like it is fairly low level network stuff. Google cloud uses sockets, not your traditional connection. stack trace below as well. Reverting to 5.11 clears it up.
var connectionString = new MySqlConnectionStringBuilder()
{
// The Cloud SQL proxy provides encryption between the proxy and instance.
SslMode = MySqlSslMode.None,
Server = String.Format("{0}/{1}", dbSocketDir, instanceConnectionName),
UserID = Environment.GetEnvironmentVariable("DB_USER"),
Password = Environment.GetEnvironmentVariable("DB_PASS"),
Database = Environment.GetEnvironmentVariable("DB_NAME"),
ConnectionProtocol = MySqlConnectionProtocol.UnixSocket,
ConnectionTimeout = 300,
DefaultCommandTimeout = 5000,
// Keepalive = 30
};