Where can i create a support ticket for an issue with MDATP (LINUX)

Hey Mark_Alkema 

Few ways you can achieve this

You can contact Microsoft Support via there phone numbers here

or you can go into the security.microsoft.com portal and on the right upper most corner there is a question mark

select that and type in some random text into the search field, and click enter

After that the "Contact Support" button should appear down the bottom to create a ticket