Does anyone know a device which can be used as a proximity sensor and can be connected to Homey? Usage is for a kitchen counter where it is not sufficient enough to know if someone is in the room. When a person comes closer to the counter light need to get more bright.

As far as I know, there is no device “off the shelf” that can do that.
You can build one your selves, using HomeyDuino, an ESP8266, or an ESP32 with a distance sensor VL53L0X. Also, a HC-SR04 Distance Measuring device can be used, but that is much bigger.