If the recent Ubuntu 19.10 wallpaper reveal has left you wanting, do check out Nostalgia.
Nostalgia a free GTK app for the Linux desktop that enables you to browse through official GNOME desktop wallpapers, and quickly set them as your desktop background.
Like Ubuntu, each new release of the GNOME desktop comes bearing its own unique wallpaper (which, again like Ubuntu, tend to stay within a loose theme).
While GNOME’s default wallpapers aren’t as well known or as revered as Ubuntu’s default wallpapers (by lieu of the fact they’re usually not used by default, i.e. so fewer people see them) they’re still high-quality pieces of art.
But if you’re bored of nature shots, bokeh, or purple gradients then switching to GNOME’s geometric backgrounds might help.
Just save yourself a safari on Google Images (with its variable image quality) and install Nostalgia from Flathub to get the original high-quality versions instead: