I don't think so I've seen any manga or manhwa covers without characters but you can find good ideas on Pinterest and use your creativity! Like adding deep meaning symbols of your plot/ plot twist with book title
I don't know about manhwa or manga, but I read a lot of novels too (mainly bl), and a lot of the danmei novel covers are pretty simple without any people, so if you feel like it you could browse through novel updates
Here's a cover from a danmei that I think is pretty: https://www.novelupdates.com/series/this-alphas-pheromones-are-exploding/
You could stylize the title that is unique to the story, or make it minimalist in a neat font. You can also add objects that is a huge plot to the story. Or make it so that the title is formed like the object. I think that even if you dont follow manga covers with the usual people in it. Make it book cover type (with title and object) itll make your manga unique and outstanding (my alltime fave cover is the shatter me series btw)
I'd recommend something from books(yes real books not manhwas) like:
A good girls guide to murder
The twisted series
You'd be home now
The totally football book
Master of the meet cute
Love is Bold
I need some inspo for a book cover but I don't know how to draw people so I wanted to know what type of covers with just words there are. Please help