Zigbee Home firmware project aims to provide similar functionality to ESPHome open-source firmware, but for Zigbee devices based on Nordic Semi nRF52 wireless microcontrollers, and later on the newer nRF53 MCUs. The firmware relies on Nordic Semi ZBOSS for Zigbee 3.0 stack and should eventually enable a range of Zigbee devices to be flashed with open-source firmware and facilitate integration with Home Assistant open-source home automation framework through ZHA integration, and support for Zigbee2MQTT is also being worked on.
No. Rpi4 can’t speak zigbee without more hardwarz.
Further down the rabbit hole I go, I suppose. Thanks!