A basic description of God includes “a superhuman being…having power over nature and human forces.” If God created nature, is outside of it, and has power over it, then He has the capability to perform a miracle (an event outside of natural laws).
You might argue that there's potentially another cause or actor (besides God) behind a supernatural event. We’re not arguing for or against that position. But even if it were true, it wouldn't negate our assertion - that if God exists (and we made the case earlier that He does), then He can do miracles. A being that was subject to natural laws (and unable to act outside them) would not be God.