I think this is a problem of unclear UI – sorry!
The Ω input can measure several different values. When you first select the channel it is measuring “Aux Voltage DC”. That’s the voltage at the Ω terminal. It is drifting because it’s a floating input with nothing connected.
If you tap the button saying “Aux Voltage DC” it will change to “Aux Voltage AC”. Tap it again and it will say “Resistance”. Then you can measure resistance at the Ω terminal.