It is required that the user you use to connect to the MySql db has access to the 'mysql' catalog and be able to select the data in it.
The reason is that that catalog contains the meta-data.
The designer queries that catalog for Meta-data retrieval, e.g. which tables / views are located in your catalog. The meta-data retrieval is done through the provider's GetSchema() method, so the actual query is constructed by the ADO.NET provider (corelab/devart).
You just need SELECT access to the meta data tables.