hey! something I noticed with your book covers is two contain a gacha cover, and while I'm not a professional writer or a salesman, I think that would make people want to read it less considering gacha is often looked down on when it comes to art forms.
if you don't one have the money or just don't want to hire somebody, you should try doing photography and adding filters to it, or try silhouettes!
photography is easy and you can get a perfect cover in the matter of a hour to 20 min depending on skill and practice, while with silhouettes you need no skill and just time and a good drawing app with at least two layers and a photo of yourself to turn into a silhouette!
just some advice! don't have to use it though!