Not able to get app roles assigned to groups

Hi, 
You can do it with Graph API, but from Powershell using cmdlets and without querying the API yourself you can do the following - 
You can use Microsoft.Graph powershell module, to get the roles assigned to a group. 

Using this function 

# Replace with your group ID or objectId
$GroupId = "<your-group-object-id>"

# Get all role assignments
$assignments = Get-MgRoleManagementDirectoryRoleAssignment -Filter "principalId eq '$GroupId'"

# Get readable role names
foreach ($assignment in $assignments) {
    $roleDef = Get-MgRoleManagementDirectoryRoleDefinition -RoleDefinitionId $assignment.RoleDefinitionId
    Write-Output "Role: $($roleDef.DisplayName) - Scope: $($assignment.DirectoryScopeId)"
}

Don't forget to connect first using Connect-MgGraph. 
If you don't have the module you can easily download it using Install-Module Microsoft.Graph