GraphQL query to find all "first-time contributor" PRs in a repo

I’d like to find out how many first-time contributors are appearing in repos, going back a few years. Not finding a way to search for this in labels, because this doesn’t appear to be a label:
Any way to retrieve all PRs with this tag through GraphQL?

This tag appears to go away from the first PR when a user makes their second PR. So I’m guessing this isn’t queryable because it’s a transient tag. :frowning: