1- The “power” to create and sustain is an attribute of essence. It is inseparable from Allah. He always has this power, and it’s his essence.
2- But using that power to create or sustain isn’t essential—meaning He can create or not create. It’s up to Him. It’s separable from His essence because at one point God did not create then He created. With power and knowledge, however, there is no such scenario. He is always knowledgeable and always powerful.