Hey @lisaspencer 

Welcome to the Klaviyo Community and congrats on your first post! Thanks for asking about creating an unengaged segment. 

One of the best things you can do for marketing is keeping your list clean, right? You are on the right track, we just need to add a little more detail to the definitions. Above I linked to a Help Center article that covers how to create an unengaged segment. The example in the article is based on 60 days (2 months) but you can just update to the following segment definition: 
If someone is in or not in a list > is > gyour main list] > and was added at least 30 days ago
AND
What someone has done > Opened Email > zero times > in the last 120 days
AND
What someone has done > Placed Order > zero times > in the last 120 days

 This will give you everyone who was added to the list at least 30 days ago and have not made a purchase or opened an email in the last 4 months. You can updated the amount of time someone was added to a list to be at least 120 days ago as well if you wanted.

Hope this helps and thank you for being part of the Klaviyo Community!

Perfect thank you!

@lisaspencer It may be what you dont have anyone in your list that has never opened an email? The issue with your logic is that it may be too restrictive.