Are you able to tell us more about this feature you are wanting to create for your store? What exactly will having a wishlist button do as well as a wishlist page? Also, may I ask why you do not want to use an app? Any information you can share will allow our contributors to find better solutions for you.
While we wait for more input, since you are using the Debut theme which is made by Shopify, and if you are on a paid plan, you can try to utilize our 60 mins of design time which you will have qualified for. This feature is for those edits you are not able to complete within the theme editor. You can reach out to our Live Support Team to see if your request is something our Themes team can help with. If they can, they will inform you how much of your 60 minutes they will be using.
If this option is not suitable however, you can also hire a Shopify Expert to help you achieve this specific feature you are after for your store. We have a good amount of trusted-freelancers that can help you with this request.
I look forward to your reply and getting more information from you.