The ESP8266, using the Tasmota firmware, sends a signal to an MQTT server running on the Raspberry Pi, which in turn translates it to a remote trigger on the Zigbee frequency with the dongle.
There are several types of ZigBee chips. Receivers are designed to receive signals or data from antennas or from other devices in the system. Repeaters are interfaces that re-transmit a weak signal ...
With that background, converting them from Bluetooth to Zigbee is not a huge leap. All that’s needed is the Zigbee firmware from [Ivan Belokobylskiy] aka [devbis] and to follow the steps put ...