How many PRs/Commits do i need merged to an open source repo for it to be impressive to pass resume screen?

I definitely agree/understand your point

(1) I'm curious to understand how much quality affects getting interviews.

Assuming the HM takes time to go through your PRs and assess the quality, I can see it making a difference. But I am not sure how many HMs actually look at the PRs being submitted

My hope is that I have heard anecdotally from friends that after sending a few (non trivial) PRs to brand name repos e.g. meta/MSFT/google the number of callbacks they got increased. But this could just be survivorship bias. I'm definitely willing to spend a few months on this

(2) I'm curious to hear anecdotally your experience with screening candidates with Open Source contributions, how often would you examine their PRs and verify quality?

I'm curious to understand how much quality affects getting interviews.

I am primarily talking about the case where you're looking for an interview from the company behind the repo - The dream scenario is that the maintainers of the repo observe your contributions over time and eventually give you a glowing referral into their interview loop.

As for companies judging outside open-source contributions, I'm unsure how those are weighed. I feel like if a hiring manager is nerdy enough to care about open-source though, they will probably ask for a reference to confirm the quality angle (instead of manually checking themselves, which is effectively impossible).

I'm curious to hear anecdotally your experience with screening candidates with Open Source contributions, how often would you examine their PRs and verify quality?

Unfortunately, I have literally never had a resume come through with meaningful open-source contributions. This is a combination of 3 factors:

1. This was back in the "good economy" days - You largely didn't need something like open-source to get some sort of job.
2. Engineers are lazy - 90%+ of engineers who are struggling in the job market frankly think only in the short-term, so they don't have the resolve to undertake something as powerful and responsible as open-source.
3. Side projects are better for most - For those who were serious about getting "extra-curricular" credit, they largely did side projects as you get 100% ownership on them and it's a solo activity (most engineers are more lone-wolf-ey). For engineers with legit side projects, I actually did spend a few minutes checking out their live deployment! I brought in many candidates into my interview loop this way.