I’ve had good experience with the Waking Up app, which is primarily Insight Meditation. If you can, a multi-day silent retreat allows you to be truly immersed in the practice of just watching your mind and all of its silliness.
I’m not understanding your comment. Mindfulness is paying close attention to the actual experiences in consciousness, as opposed to just being carried along by thoughts. It’s not about taking control of your mind.
Mental illness is treatable, and being aware of the symptoms as they’re happening is a major part of the treatment for many such illnesses.
Mindfulness. You may not be able to turn off the (insert negative feeling here), but you absolutely can turn off the suffering.
I have no doubt some people struggle more than others to get to the point where they can sit back and watch. It wasn’t immediately obvious to me either, but a couple of months of short daily practice enough to start seeing what the fuss was.