Add a DL as a login in azure sql managed instace
To create a DL (assuming it is a group in AAD), you need to create without the @domain.. on the database that you want to connect.. example:

CREATE USER [GroupName] FROM EXTERNAL PROVIDER

Here you have a link

https://techcommunity.microsoft.com/t5/azure-database-support-blog/lesson-learned-23-how-to-add-aad-security-groups-to-azure-sql/ba-p/368866