public void ConfigureServices(IServiceCollection services)
{
    services.AddMvcGrid(filters =>
        filters.Register(typeof(Int32), "contains", typeof(NumberContainsFilter)));
}

public class NumberContainsFilter : AGridFilter
{
    public override Expression? Apply(Expression expression, CultureInfo culture)
    {
        if (Values.Length == 0 || Values.Any(String.IsNullOrEmpty))
            return null;

        return base.Apply(expression, culture);
    }

    protected override Expression? Apply(Expression expression, String? value, CultureInfo culture)
    {
        Expression valueExpression = Expression.Constant(value?.ToUpper());
        MethodInfo toStringMethod = typeof(Int32).GetMethod(nameof(Int32.ToString), new Type[0])!;
        MethodInfo containsMethod = typeof(String).GetMethod(nameof(String.Contains), new[] { typeof(String) })!;

        Expression toString = Expression.Call(expression, toStringMethod);

        // (x) => x.ToString().Contains(value)
        return Expression.Call(toString, containsMethod, valueExpression);
    }
}