How do I get started with multi-agent reinforcement learning? Is there any tutorial that walks through a multi-agent reinforcement learning implementation (in Python) using libraries such as OpenAI's Gym (for the environment), TF-agents, and stable-baselines-3?
I searched a lot, but I was not able to find any tutorial, mostly because Gym environments and most RL libraries are not for multi-agent RL.
After checking the Internet, you will probably find several resources such as

https://github.com/mohammadasghari/dqn-multi-agent-rl
https://rlss.inria.fr/files/2019/07/RLSS_Multiagent.pdf
https://arxiv.org/abs/2011.00583
and others.

Try to understand the principles first (see above). After some reasonable amount of coding you can adapt OpenAI gym.
Good luck!