The Portalist recently curated a list of 25 Must Read Space Operas. Diving into a subgenre like this is another way to showcase your collections' backlist in a book display or book list. The Encyclopedia of Science Fiction defines a space opera as: "colorful action-adventure stories of interplanetary or interstellar conflict." (This page also includes the names of many of the authors who have worked in the subgenre.) These are not books with hard science throughout and may instead include more fanciful ideas of technology. These sprawling, epic adventures can be humorous or have romantic subplots. Goodreads has lists of titles as well a definition and related subgenres. Reactor has tagged their related articles and lists with space opera as well.
There are a lot of series that would fit into this sort of display or list. There is also ample opportunities to promote diverse books and authors within this subgenre.
You can include a definition on signage as well as links to online resources on your display.
Add audiobooks and DVDs of movies from your collection that fit the theme as well. If you have local or library based book displays that focus on science fiction, promote them as well on the display.
Here are some lists to get you started on your own space adventure!
Book Riot has a list of 25 of the Best Space Opera Books of All Time and 10 Space Opera Series to Get You Through The Winter
Bookish Brews - 20 Best Diverse Space Opera Books You Need to Read
The Fantasy Review - 7 Modern Space Opera Novels That Will Take You On Epic Adventures
Publishers Weekly - 10 Authors Shaking Up Space Opera
If you want to explore sci-fi subgenres further, The Portalist has a guide to get you started: Powerful Sci-Fi Subgenres That Every Geek Needs to Explore.