hi, like @thex was already pointing out. The MqttDimmer has only a slider to set the brightness, no on/off switch. For that you need to a MqttSwitch.
The config with 1 MqttDimmer and 1 MqttSwitch will probably work.
{
"brokerId": "your-broker",
"topic": "shellies/shellydimmer-keuken/light/0/set",
"resolution": 101,
"message": "{\"turn\": \"on\", \"brightness\": value}",
"stateTopic": "shellies/shellydimmer-keuken/light/0",
"stateValueKey": "brightness",
"id": "your-id",
"name": "your-name",
"class": "MqttDimmer"
},
{
"brokerId": "your-broker",
"topic": "shellies/shellydimmer-keuken/light/0/command",
"onMessage": "on",
"offMessage": "off",
"stateTopic": "shellies/shellydimmer-keuken/light/0",
"id": "your-id",
"name": "your-name",
"class": "MqttSwitch"
}
The message format is what you see in config.json. In the MqttDimmer device config message field you enter: {“turn”: “on”, “brightness”: value}