Then the target_sensor should be a thermometer in the room, and target_temp is the temperature you expect there

But the TRV is climate type by itself. so, I'm not sure how to control it by PID.

As I can see, there are different TRVs around, so possible workflow depends on what you can control. Is there manual on/off mode for your TRV? Do you have additional thermometers in your rooms?

I'm using this one (link below). I'm planing to add extra temperature sensors. but the TRV have temp sensor too.
As I can see, there is no option to on/off the TRV, only regulate the temperature.

trv - Aliexpress

So, if you're going to use TRV temp sensor, then it will just work, you don't need Smart Thermostat.

If you add extra sensors - just look at TRV and "external" sensor difference and then you can adjust TRV target temp by Smart Thermostat to compensate this difference. Or leave it as is if the difference is minor.