Hi @Simon_B,
Check my reply in this thread: Show Roles in users grid is always empty - #6 by korchev
You need to set the Template as well. Probably
<RadzenDataGridColumn TItem="Employee" Property="Employee.Roles" Title="Roles">
<EditTemplate Context="employee">
<RadzenDropDown @bind-Value="@employee.Roles" Data=@roles TextProperty="Name" Multiple=true AllowClear=true Placeholder="Roles"></RadzenDropDown>
</EditTemplate>
<Template Context="employee">
@string.Join(", ", employee.Roles.Select(r => r.Name))
</Template>
</RadzenDataGridColumn>