I'm betting that 90% of the time a horizontal pocket on jeans is a placket pocket, that's part of why it's so hard to find the term you're looking for. That said, I was able to figure it out: you want "slash pocket" or "welt pocket" jeans (https://www.amazon.com/Frame-Womens-Flare-Pocket-Jeans/dp/B09MV56W7J). If you don't find enough useful reference images, know that the pocket is really unlikely to be deeper than 2cm so the extra fabric inside won't extend far