Ask HN: How do I found OSS project that don't commerical backing?

Lately, I've been thinking that a great way to upskill would to find an OSS project that I find interesting and jump in. However, I am not sure what to feel to contribute to project that already have commercial backing.

Do people contribute to project that already have full time employee to build them? I honestly don't know how this is suppose to work.

For instance, I kind of want to know how these AI assistant VS code extension work, for example, Cline, Roo Coder, Kilo, etc. Yes, their source code is available but I believe for me to fully grasp the system, I will need to make an attempt to code. However, these project seem to have commercial backing.

Does it make sense to contribute to them vs project built by someone in his free time for fun? For example, this comes to my mind

https://github.com/unknownskl/greenlight