Using Classic Outlook on Windows for personal email, calendar, and contact management
Hi! This happens because Office Home 2024 does not include Outlook, so the issue is not really the default-app setting. Microsoft’s Office 2024 FAQ shows that Office Home 2024 includes Word, Excel, PowerPoint, and OneNote, while Outlook is included with Office Home & Business 2024 or can be installed as a standalone product. That is why Classic Outlook can open but then shows the Product Notice and sends you into the update loop: the app is there, but the current license does not activate it.
So, if you want Classic Outlook as your default mail app, you will need a license that includes it, such as Outlook standalone, Office Home & Business 2024, or a Microsoft 365 subscription that includes desktop Outlook. Otherwise, with Office Home 2024, the supported option is to use new Outlook as the default mail app.