There are a few factors here, but it’s most likely up to the laws in your country, and as far as I know, most countries do allow (or at least not explicitly ban) you to sell AI generated content, but some countries have laws which don’t allow you to claim copyright over that content - meaning that you’re allowed to sell it, but you couldn’t e.g. prevent others from copying your book cover image and using it in their own work.

The law in this area is gray, at best, but law is interpreted and a court case could go either way depending on how convincing the arguments deployed are.

Your question is actually

If I got sued, would I win?

And nobody can tell you that, not even a lawyer - they could take an educated guess, but that’s it. So the real question you need to answer is:

Am I willing to take the risk that I could be sued for copyright infringement for using this image, knowing that I might or might not win the court case?

And of course, only you can answer that. So… are you?