Allow a list creation filter which allows you to show all users who opened any email assigned to a specific campaign. Would save a lot of manual entry for accounts with large volume of emails.
@shannonziggy take a look at this and upvote please! https://community.hubspot.com/t5/HubSpot-Ideas/Select-HubSpot-marketing-campaign-in-a-list-filter/idc-p/419838#M77388