I run 100-device zigbee network with zigbee2mqtt. Philips, Bosch, Sonoff and some others. No internet access.
Zigbee devices are slow and low power, they cannot access internet directly.
Zigbee devices are slow and low power, they cannot access internet directly.
I guess a bridge vendor could pull the rug on the antenna ("your Sonoff zigbee antenna is now only compatible with Sonoff zigbee product")(to be clear: they've never done that), but the format is open enough that there's ton of alternative suppliers and open source bridge (the aforementioned zigbee2mqtt).
In any case, I've got a good amount of both Ikea tradfri and Philips Hur bulb and they have never contacted an Ikea or Philips hardware or software of their life.