Extension method which excludes any properties derived from the specified base class from being serialized into JSON.

ExampleUsage.cs

private class ExampleA 
{
    public string PropertyA { get; set; } = "not wanted";
}

private class ExampleB : ExampleA
{
    public string PropertyB { get; set; } = "wanted";
}

// ...

var options = new JsonSerializerOptions
{
    TypeInfoResolver = new DefaultJsonTypeInfoResolver()
        .ExcludePropertiesFromType<ExampleA>()
};
var json = JsonSerializer.Serialize(new ExampleB(), options);
// Should produce JSON: {"PropertyB": "wanted"}

JsonSerializerExtensions.cs

public static class JsonSerializerExtensions
{
    public static DefaultJsonTypeInfoResolver ExcludePropertiesFromType<T>(this DefaultJsonTypeInfoResolver resolver)
    {
        return resolver.ExcludePropertiesFromType(typeof(T));
    }

    public static DefaultJsonTypeInfoResolver ExcludePropertiesFromType(this DefaultJsonTypeInfoResolver resolver, Type type)
    {
        if (resolver == null || type == null)
        {
            throw new ArgumentNullException();
        }

        var exclude = type.GetProperties().Select(x => x.Name).ToHashSet();

        resolver.Modifiers.Add(typeinfo =>
        {
            if (typeinfo.Kind == JsonTypeInfoKind.Object && type.IsAssignableFrom(typeinfo.Type))
            {
                foreach (var property in typeinfo.Properties)
                {
                    var name = property.GetMemberName();
                    if (name is not null && exclude.Contains(name))
                    {
                        property.ShouldSerialize = static (obj, value) => false;
                    }
                }
            }
        });
        return resolver;
    }

    public static string GetMemberName(this JsonPropertyInfo property) => (property.AttributeProvider as MemberInfo)?.Name;
}