If no one else is selling your topic… abandon it
Please be aware of this upfront.
Some writers tell me “I want to find an idea that’s brand-new and original, I don’t want to compete with everything else that’s out there.”
Unfortunately much as you might want to be totally “original”, and to avoid competition, if the topic you’re thinking about has never sold online there is very little chance that you will be able to do it. Stick to creating products in those areas in which there are already a mass of products which are selling.
Are other books on your topic selling well? That's a big clue that your book will sell too.