Hi Samarth,
I’m the mentor for one of the proposed projects (E2E tests for the p5.js web editor)
While contributions to the Processing repos is not necessary for your application, I would recommend getting a feel for the repos for the potential projects so that you can assess which one feels the most interesting/fun/familiar to work on! For me, that usually means creating a fork and playing with things locally to get a feel for the codebase, and maybe seeing if I can resolve any of the “good first issue” locally.
I think in terms of approachability for a JS/TS dev, the documentation sites would have the more modern, youtube-able stacks. The p5.js web editor repo is a bit more antequated.