@charlesthivierge-5859 Thanks for reaching out. Unfortunately, currently the on-prem groups can not be used for assigning Azure AD built in or custom roles.
The same has been called out here : https://learn.microsoft.com/en-us/azure/active-directory/users-groups-roles/roles-groups-concept
We will be extending this to On-prem groups as well in future (https://techcommunity.microsoft.com/t5/azure-active-directory-identity/assigning-groups-to-azure-ad-roles-is-now-in-public-preview/ba-p/1257372)
It has following limitations (not supported) :
Assign cloud groups to Azure AD custom roles
Assign cloud groups to Azure AD roles (built-in or custom) over an administrative unit or application scope.
Assign on-premises groups to Azure AD roles (built-in or custom)
Also have a look at known issues about this here : https://learn.microsoft.com/en-us/azure/active-directory/users-groups-roles/roles-groups-concept#known-issues
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