Empty it, put a cover on it and put some plants in pretty pots on top of the cover. Cover could be as simple as a piece of plywood cut in the appropriate shape and painted a color similar to the general area. Or you can go large and make it/paint it to be waterproof and longer lasting.

Is this in a bed area? (BTW, when you provide photos, it's best to start with ones that include surroundings so people can get a feet for how the whatever is sited.) If it's in a bed area, I would rent a jackhammer and break out the bottom of the pool, while not damaging the sides/back/front. THEN, you can put soil in it and plant flowers/groundcover. The failing in your earlier attempt is that soil must drain and it can't in a pool.