What did the supreme Buddha develop to reach enlightenment?

That would be the 4 noble truths.

The Buddha, Siddhartha Gautama, developed the Noble Eightfold Path—a concise path to enlightenment. It consists of Right Understanding (grasping Four Noble Truths), Right Intention (cultivating wholesome intentions), Right Speech (truthful and compassionate communication), Right Action (ethical conduct), Right Livelihood (honest work), Right Effort (continuous self-improvement), Right Mindfulness (present-moment awareness), and Right Concentration (meditative focus). The Buddha's own enlightenment under the Bodhi tree marked his liberation from suffering and rebirth, and he dedicated his life to teaching others this transformative path to awakening.