It’s difficult to make the commands as convenient as possible on all systems. The most common way people use Prodigy is to install it into a virtual environment, since that avoids modifying your system. When installed into a virtual environment, it’s best to use the command “python”, to make sure we’re calling the correct interpreter.
You might try executing the command explicitly with python3 -m prodigy, to make sure you’re running the right command on your system.