Hello Pedro, thank you for your interest in my post.

You can install it by using the below command

$ pip install gym[all]==0.18.0

You could meet some errors related to Mujoco. I am not sure which part of the Gym is needed for the Pong environment now.

After that, you are required to download the ROM file from https://github.com/openai/atari-py#roms.

You need to register the ROM file using the below command after you extract the downloaded ROM folder.

$ python -m atari_py.import_roms <path to folder>