It's going to take me a bit of meandering to get to my actual point but I promise this is somewhat going somewhere, I'm just trying to summon my knowledge on art and design after midnight which always gets "interesting".
I'll use some covers/icons I designed for my own novels as an example.

This is my cover for The Princess and the Squire. It shows the main characters rather small in comparison to the rest of the image around them, showing their world. This is because it suits the theme of the girls (or mostly the princess) finding their place in the world and their happiness. It's a light and fluffy novel, set in a fairy tale world, so this cover gets you right in the mood for that.

And this is the cover for The Demon and the Exorcists. It's a slightly different approach; because the bulk of the novel uses first person perspective, I pictured the main character quite large, but pictured the imminent danger he's in as well, even if it's not exactly clear who it is. It uses a bit of an anime-y style and it has a nice pop of contrast and contrasting colours, so I personally like how it comes off the page (or rather, screen).
The thing is, though, during posting periods, these novels perform about equally well as far as I'm aware, which leads me to believe that honestly, it doesn't really matter what the art on your novel is or what style it was made in, as long as it
- says something about your story,
- matches the general vibe of the story you're telling,
- looks appealing,
and yes, that can mean "words on a solid color background", given that the typography is well-designed. But really, I've seen popular novels on this website use anything from typography to abstract shapes to moody photography/photomanips. Your cover could be anything.
Just let your imagination go nuts, but above all, try stuff out! Canva seems to be a nice online tool to get you started if you can't/don't want to invest in the expensive stuff and there are many free resources on design as well.
Anyway, I hope this was at all useful/helpful. Good luck, and have fun designing!