"The given key 'utf8mb4' was not present in the dictionary

i have a problem with sql in C#.

I try to use ExecuteReader(), i get an error in this line:

MySqlDataReader reader = readcmdQuery.ExecuteReader();

System.Collections.Generic.KeyNotFoundException
  HResult=0x80131577
  Nachricht = The given key 'utf8mb4' was not present in the dictionary.
  Quelle = System.Private.CoreLib
  Stapelüberwachung:
   at System.ThrowHelper.ThrowKeyNotFoundException[T](T key)
   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
   at MySql.Data.MySqlClient.CharSetMap.GetCharacterSet(DBVersion version, String CharSetName)
   at MySql.Data.MySqlClient.MySqlField.SetFieldEncoding()
   at MySql.Data.MySqlClient.MySqlField.set_CharacterSetIndex(Int32 value)
   at MySql.Data.MySqlClient.MySqlField.SetTypeAndFlags(MySqlDbType type, ColumnFlags flags)
   at MySql.Data.MySqlClient.NativeDriver.GetColumnData(MySqlField field)
   at MySql.Data.MySqlClient.NativeDriver.GetColumnsData(MySqlField[] columns)
   at MySql.Data.MySqlClient.Driver.GetColumns(Int32 count)
   at MySql.Data.MySqlClient.ResultSet.LoadColumns(Int32 numCols)
   at MySql.Data.MySqlClient.ResultSet..ctor(Driver d, Int32 statementId, Int32 numCols)
   at MySql.Data.MySqlClient.Driver.NextResult(Int32 statementId)
   at MySql.Data.MySqlClient.MySqlDataReader.NextResult()
   at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader(CommandBehavior behavior)
   at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader()
   at decustomer___LAP_Projekt.MainWindow.MySQLConnector()

I thought it was a problem with Visual Studio or XAMPP.

I tried - add CHARSET=utf8 to the connection string - changing the "utf8mb4" to "utf8_german2_ci" in database - Execute SET NAMES 'utf8' - Updating MySQL - Tried on other client - Set up a new mysql server with MySQL Installer 8.0.20 (before: xampp)

The code snippets:

string connStr = CreateConnStr("localhost", "xxx", "root", "");
MySqlConnection connection = new MySqlConnection(connStr);
connection.Open();


public static string CreateConnStr(string server, string databaseName, string user, string pass)
        {

string connStr = "server=" + server + ";database=" + databaseName + ";uid=" +
user + ";password=" + pass + ";CHARSET=utf8;pooling=false;Allow User Variables=True";
return connStr;
        }
...
string readcmdQuery = "SELECT id, vorname, nachname FROM berater;CharSet=utf8;";
sqlcmd.CommandText = readcmdQuery;
MySqlDataReader reader = readcmdQuery.ExecuteReader();
consList.Items.Clear();
while(reader.Read())
...

Please help me. I don't found other solutions in the internet.

It seems like you might be using a very old version of MySql.Data; the problem you're reporting sounds like bug 58244, which was fixed a long time ago.

Or perhaps you've found a slightly different variant of that bug that manifests under slightly different conditions. If so, you could report it at https://bugs.mysql.com/ and wait for a fixed version.

However, I would recommend uninstalling MySql.Data and installing MySqlConnector instead. It's supported utf8mb4 from the beginning, adds async support, and fixes many other bugs.