The images I created myself keep coming up as 'similar'—I don't know what to do.

Same for mine. Some really great ones, rejected. The algorithm or bot, or whatever, is extremely broken.

Read the Popular Subjects sections from your Contributor User Guide for more ideas.

https://helpx.adobe.com/stock/contributor/submit-your-content/submit-photos/photo-submission-overview.html

Most customers are interested in images of real people in real situations, interacting with other people and objects. Think about people at work, play, school, home, travel, healthcare, etc...

Hope that helps.

There are half-a-billion abstract images, backgrounds & wallpapers available on Stock and free websites.  You’ll never find a buyer for these. There’s too much competition.

If you want to avoid refusals for “similar content,” work on content that’s more realistic and has some commercial value to advertisers and marketers.

Case in point after a search: “39,792,363 results for abstract background and wallpapers.”

It’s useless to try to compete against these numbers even if your assets were accepted.

There are millions of abstract backgrounds already available on Adobe Stock. You need to submit more unique material.