I don't know if this is exactly the kind of thing you're looking for, but there are a few sites that aggregate open source project tasks tagged as "good first issue" / "help wanted" - for example these two (that confusingly have very similar names):
Would also recommend checking hacktoberfest topic (the event itself happens in October, but the topic is still a good reference), which is used by repos whose owners explicitly encourage contributions, especially from people with less contributor experience.