Q: The readout is not accurate when ITC-100 is connected to K probe/PT100

A: Please remove the probe, put the PID in a stable temperature place, then use a wire to connect #3 & #4, set Sn= 0.

Can it read room temperature correctly (there may be ±5℃ difference)?

Sorry to jump someone else’s thread.
But when I do as suggested, above, I get 0.0 as my reading.
Sn set to zero everything else, as default.

If your wiring is the same as the example diagram, but the controller reading is far off from room temperature, it may be a problem with the controller.
If the controller is within the warranty period, please contact the seller with photos of how you wired it and order information so that they can do further after-sales processing.