Those settings have been independent before. You could set a sub crossover frequency of e.g. 200 Hz and configure RC to correct from 20 Hz upwards. However, the behaviour that most of us have been observing (after RC had become official on Android) was that automatic RC would not attempt to apply any correction below 200 Hz in this example.
Now we have the switch:
View attachment 10442
Subwoofer calibration is enabled by default. RC should apply correction according to the frequency range configured above.
When disabled it should ignore the frequencies below the subwoofer crssover frequency defined in the app.