what is the recommended way to handle opt outs? We have many lists and ideally, I think when someone unsubscribes, it does so to every list they belong to. We’d like to give people the option to unsub from only the lists that they want to unsub from.

The best way to do this is to add a link to your emails in a given campaign that says “I’m not interested in these emails”
Have that tag them indicating that they are not intersted in that specific topic and remove them from the campaign.
Take them to a landing page that indicates that you will remove them from that list.

This helps to keep them from unsubscribing from everything.