Does not accept images due to similarity

are all your assets so grainy? 

Stock already has gazillions of backgrounds & wallpapers.  Find some other niche to fill.  This one is oversaturated. 

If you need inspiration, see my previous reply below.

https://community.adobe.com/t5/stock-contributors-discussions/looking-for-inspiration-what-to-submit-was-hi/m-p/13554283#M53434

Good luck.

There are already nearly 52 million images in the database tagged with "green background". The likelihood that a Buyer would ever find or license one of your files is essentially zero. That's probably why Adobe rejected it based on on "similars". Search the Buyer portal to see what your competition is.

I think Adobe has received more than enough textured gradient backgrounds, hence the "similarity" issues. Backgrounds and wallpapers can be easily made for free by even individuals with little or no AI experience, and there are thousands if not millions of such assets available, also for free, throughout the internet. To solve the problem, submit more unique and varied assets.