When Satoshi Nakamoto mined the genesis block on January 3, 2009, the reward was indeed programmed in the protocol to be 50 BTC, but those bitcoins could never be spent.

📜 Key Details

Theoretical Reward: The genesis block included the reward of 50 BTC, as defined in the Bitcoin code.

Inaccessibility: Due to how that first block was designed, the reward cannot be transferred or spent. It is a technical effect of the initial code.

Subsequent Blocks: Starting from block 1, the rewards were indeed usable, and thus began the real circulation of Bitcoin.

👉 In summary: Satoshi Nakamoto could not use the 50 BTC from the genesis block; it was from block 1 that the rewards began to be effective.