The subject cannot be saved as a separate image in Lightroom because you are working with a single image. What process are you using that makes you think you are saving the subject with the white background as a separate image?
In this case, I am wanting to save this image with the background removed via the masking feature. Is there a way to actually remove the selected area and make it white, instead of simply masking the area off? I'd like the background to be removed.
Might be expecting too much from the feature, but since it can select the subject, why not be able to remove the background based on what it detects as the subject.
Well, you just haven't finished the job. Unfortunately, I'm not the one to tell you how to finish it because I'm still learning. There are tutorials on YouTube that you might want to go watch. And keep watching this thread because someone who has learned the new masking process that is that I have can tell you what needs to be done to finish what you are wanting to do. Sorry, I just can't take you where you need to be.