Knowing that B4XPreferencesDialog doesn't support this feature, how do you achieve something like this in B4A (or do you know some crossplatform solution)?
I've thouthg in a webview, but it's not probably the best solution
There is nothing special about this layout. You can create create multiple layouts and load the correct one to a panel beneath the Spinner / B4XComboBox.
Another option is to let the user select the "form type" and then show the relevant form with B4XPreferenceDialog.