I knew It was the best Coke...

McDonald's Coke tastes different due to a combination of factors, including syrup delivery, temperature control, syrup-to-water ratio, and straw design. McDonald's receives its syrup in stainless steel tanks to maintain freshness.
They also pre-chill both the syrup and filtered water before dispensing, which helps maintain carbonation. Additionally, the syrup-to-water ratio is adjusted to account for melting ice, ensuring a consistently strong flavor.

Finally, McDonald's uses wider straws to enhance the flavor experience.

I googled it.