Is it possible to make one of the items in the Data List the default option via the interface?

via the UI, no, afraid not. It's a much requested feature, but it's not something I'm looking to add to Data List (at the moment). Some background reading on my thoughts about setting default values in data-type configuration... - https://github.com/leekelleher/umbraco-contentment/discussions/91#discussioncomment-621301 - https://github.com/leekelleher/umbraco-contentment/discussions/224#discussioncomment-2876772 - https://github.com/leekelleher/umbraco-contentment/discussions/309#discussioncomment-5180608

Thanks @leekelleher, similar to our text and image fallback it's so the user knows a default is being applied and which item it is. But I'm sure you know that. Also sure you have plenty other priorities right now so thank you for taking the time to reply. I'll have a read through your links.