Every designer sketches. It's part of the creative process for most of us. For me I sketch endlessly, and about way more things than design projects. I create patterns for leather and sewing, plan furniture designs, cabin builds, maps of places I want to remember, logos to things that will never exist, jewelry designs, sketch notes, hand lettered shenanigans, literally endless sketching. I fill up about 3 moleskins and 1 full size sketchbook a year.
Here's a few snaps of the things that are remotely worth looking at (I'll admit some of it looks like my pencil had a seizure.) Some are hanging in my studio, some are still in books, some are very half baked but it's important to make the art process, art as well. And there's worse things than having too much art.
You can always find a more current steam, of finished projects and sketched on my Ello.co page