Having floating poop is not always bad as sometimes it may just be caused by something your ate that caused the poop to contain more gas which causes the poop to float.
But if your poop continues to float and not sink then it could be bad and could be caused by Malabsorption.
Greasy stools that are foul smelling may be due to severe malabsorption, particularly if you are losing weight. Malabsorption means your body is not properly absorbing nutrients.
Another cause of floating poop is A gastrointestinal infection so if your poop continues to float and doesn't start sinking after a few times you poop then I would let a doctor know about the floating poop as they can test you for those problems.
Poop should normally sink in the toilet after it leaves your body so it would be good to get checked out just to make sure nothing is wrong.