Same question and answers as this other thread here → Zigbee Utilization 90%, normal for 130 devices?
You can have 200 Zigbee 3.0 or there about (and even if more older Zigbee devices as their lower security have less overhead) but that depends on you having enough Zigbee Router devices and avoid EMF interference, see → Zigbee networks: how to guide for avoiding interference and optimize for getting better range + coverage