To get all meta-reviews for a venue, you can do the following:
Get all submissions for your venue. You can do this by passing your venue's submission invitation into get_all_notes. You should also pass in details = "directReplies" to obtain any Notes that are a direct reply to each submission.
2. For each submission, add any replies with the Meta-Review invitation to a list of meta-reviews.
meta_review_name = venue_group.content['meta_review_name']['value']
meta_reviews=[openreview.api.Note.from_json(reply) for s in submissions for reply in s.details['directReplies'] if f'{venue_id}/{submission_name}{s.number}/-/{meta_review_name}' in reply['invitations']]
3. The meta_reviews list now contains all of the meta-reviews for your venue.