Yes, you can use the internal sensor to control the temperature and the external sensor to do the floor overheating protection(optional). Or you can use the external sensor to control the temperature, at which point it will no longer be used for floor overheat protection detection. This sensor option function is supported by Meross app.
You can install the MTS200(for boiler/water system version) with your system according to the diagram below. The sensor connected to terminal 6,7 is optional. You can also follow up the Meross App step by step to set up your system.
Gas boiler heating system.(Control the boiler with thermostat)
Water underfloor heating system(Control the thermal actuator
with thermostat, support both 2-wire actuator and 3-wire actuator).