if you create a template sensor you can use this as the tempsensor!
- name: wz_temp_mean
unique_id: wz_temp_mean
unit_of_measurement: '°C'
state_class: measurement
device_class: temperature
state: >
{{((states('sensor.t_h_sensor_wz_temperatur') | float(0) + states('sensor.thermometer_zig_temperatur') | float(0)) / 2) | round(1)}}