My Mom had a whole set of molds like these that I’m pretty sure she got with some kind of Jello box top deal. She probably set in Jello box tops with 50 cents for every one or two of them. But Ralph is correct, they were originally meant for Jello molds.
I would use a yeast bread recipe, or a quick bread recipe that had a fairly stiff batter, and a fair amount of oil or fat in the recipe. There is a lot of detail in the bottom of that mold, places for a cake to stick, but I think it can be done. I’d give it a whirl at least once.
Eddie