In the following reproducible, try filtering the third column (SomeNavigationProperty.Field1). It does not work.

<TelerikGrid Data="@myData" Pageable="true" Sortable="true" FilterMode="@GridFilterMode.FilterRow" Groupable="true">
    <GridColumns>
        <GridColumn Field="@nameof(SampleComplexObject.ID)" Title="ID"></GridColumn>
        <GridColumn Field="@nameof(SampleComplexObject.Name)" Title="The Name"></GridColumn>
        <GridColumn Title="First Nested Property" Field="SomeNavigationProperty.Field1" />
        <GridColumn Field="SomeNavigationProperty.OtherField" />
    </GridColumns>
</TelerikGrid>


@code {
    public class SampleComplexObject
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public NestedObject SomeNavigationProperty { get; set; } // use this field name for data binding
    }

    public class NestedObject
    {
        public int Field1 { get; set; }
        public string OtherField { get; set; }
    }

    public IEnumerable<SampleComplexObject> myData = Enumerable.Range(1, 50).Select(x =>
            new SampleComplexObject
            {
                ID = x,
                Name = "Name " + x,
                SomeNavigationProperty = new NestedObject
                {
                    Field1 = x,
                    OtherField = "second " + x % 6
                }
            }
        );
}