If I use Mail as the "Open with", it will start to open the file with the Mail app, but as the switch is set to "new Outlook", it then switches into the new interface wich closes the file.
I tried setting the "Open with" to use the "new Outlook" located here;
C:\Program Files\WindowsApps\Microsoft.OutlookForWindows_1.2023.1018.300_x64__8wekyb3d8bbwe\olk.exe
Windows added the "new Outlook" option to my "Open with" menu, but when it opens I get the following Popup;

When I switch to the Classic Outlook for Windows, I am able to view the .EML files, my only fear is that when the Classic Outlook for Windows is depreciated and we are forced to use the New Outlook for Windows, we will lose this functionality. Emails are saved to our CRM, and if we need to view them they have to be downloaded to the users PC, so emailing them to yourself so you can read them several times a day as a workaround is an extra step and a very inefficient use of people's time.
I do hope the development team is aware, and will remedy the situation prior to the depreciation of the Classic Outlook for Windows.