The challenge's main requirement is to build or update a functioning Microsoft Graph-powered solution that improves productivity. Solutions must be an Office 365 add-in, Teams integration, SharePoint solution, or Outlook solution. The focus is on cloud-based solutions and the prizes are for the best of each of those types (Office 365 add-in, Teams integration, etc.) so I'd encourage you to make it web-based rather than desktop.
If you have more specific questions on your idea that you don't want to post publicly, feel free to email me directly stefanie @ devpost . com :)