Not knowing what Zigbee device you are using, it’s unclear whether you have a switch, which has a state of either on or off, or a button, which is just a momentary “press” to do something, and is not itself on or off.
If the Zigbee device is a switch, i.e. showing on/off in the Web UI, I prefer to use a blueprint to quickly create an automation to sync the switch’s state to the tasmota relay.
If the Zigbee device is a button with no state, i.e. showing “Press” in the Web UI, you can create an automation that fires when the button is pressed and calls “switch.toggle” service for the relay.