See https://opensource.guide/how-to-contribute/ - section 4 has handy links to find projects
Pandas is pretty friendly project to contribute to...
Maybe just browse the npm packages that are popular. Find one you like and has open issues in Github.
Maybe Django or Certbot?
Come help out with Apache Airflow! It's a great project to get involved with because it has a ton of users and real world problems, but it's still early enough that there's low hanging fruit in terms of adding functionality and improving existing code.
A helpful place to start is the provider packages, since Airflow has integrations with so many 3rd party providers, and if you have knowledge in any of them it can be a good jumping off point.
https://github.com/apache/airflow/