There are plenty of neko wallpapers that will scale to that resolution. just download and set as background etc. unless its site specific which you can take a favourite wallpaper and and downscale in a photo editing app.
but also id like to see a reference example of a tag that shows up when used in prohibited. i am thinking you are seeing something relative in the images but the photo you are looking at doesnt actually have the tag you are prohibiting.
You use the prohibited tags section. although you have to be specific on some things, like if its not wanting to see a male you will have to put boy, male, etc. at least thats what i think. i am pretty sure the tag vocabulary is limited but im not sure how far