Use Variables in the sql connectionstring

It's not possible within that dialog. However you can use ADO Object and create your own connection string using variables e.g.

function ADOExample()
{
    var AConnection = ADO.CreateConnection();
    var dbServer = "Server1";
    var dbName = "ALPHA";
    AConnection.ConnectionString = "Provider=MSOLEDBSQL19.1; Integrated Security=SSPI; Persist Security Info=False; Initial Catalog=" + dbName + "; Data Source=" + dbServer + "; Use Encryption for Data=False;";
    AConnection.Open();
   
    // Do something
   
    AConnection.Close();
}