Latest Build of ffmpeg Isn't Working
I'm guessing you downloaded the source code instead of ffmpeg.exe. FFmpeg only provides source code so you have to download it from third-party sites if you don't want to compile it.
See the FFmpeg Download page, go to the Get packages & executable files section, and choose your OS.
For Windows you can get ffmpeg.exe from:
- gyan.dev
- BtbN
These are not some random sites as both providers are known in the FFmpeg community.