This is an accepted solution.
My name is Rae, and I work for Shopify.
Thanks for posting about the menu on the mobile version of your Debut theme. I tested this out on my end using the URL you provided, and I also experienced the same issue. Not to worry though, I'm happy to help provide some next steps to get this resolved!
Have you recently made any coding changes to your site, or downloaded an app that required coding? If so, this may have impacted the menu on your theme, so I recommend reaching out to the app developers who built the app you're using. That way, those developers can investigate their coding to determine if it's related to the issue with your menu.
However, if you haven't made coding changes, or downloaded any apps recently, this is something our team can help investigate since you're using a Shopify-developed theme. To start this process, please visit our Help Center, log in to your Shopify account, and submit a support request with us there. This will authenticate your account so that our team can speak with you about this via email, live chat, or through a callback.
Once you're in contact with our team directly, please let them know that the menu on the mobile version of your Debut theme won't open. Providing this information to our Support team right away will ensure we can get your question sent to the correct team, and get your theme looked into as soon as possible.
These steps should help resolve things for you, so I've marked my reply as the solution to this thread. This will hopefully benefit other Community users who are experiencing this same issue, as it outlines what steps they can take to reach a resolution, too.
Let me know if you have any further questions or concerns, and I'll be glad to continue lending a hand!