You should mention that you already posted this question on Stackoverflow: <https://stackoverflow.com/questions/76611371/execution-time-of-recursive-fibonacci-function-is-slower-in-c-than-equivalent-ni/76611867>
It has already been pointed out there that your environment (Mingw, Windows, gcc 8.10, different CPU, etc.) is not directly comparable to the results published in the repo (Linux/docker, gcc 9.3.0, etc.).
