Google Assistant: In the Google Home App, some devices are displayed with a light bulb and others with a socket symbol, how can the symbol be changed?

All devices labelled with a light bulb are categorised as lamps or lights, so you can simply say: "Hey Google, switch off the light".

Dimmers or Zigbee lamps that are registered on the gateway are automatically in the Lamp category.

Depending on the name used, switch actuators are sometimes categorised as switches. You can select the device in the Google Home App and then manually change the device type to lamp in the configuration.

After saving, this device is also activated when the command "Hey Google, switch off the light" is given".