public class SettingsCall : ApiCall
    {
    }

    public class SettingsResponse
    {
    }

    protected TResponse Call<TResponse>(ApiCall call) where Rp : class
    {
    }

    Call<SettingsResponse>(new SettingsCall{});

    public class SettingsCall : ApiCall
    {

        public class Response
        {
        }
    }

    // чтото типа такого - получить тип респонза както автоматически
    protected TCall.Response Call<TCall>(TCall call) where ....
    {
    }

    // чтобы потом
    Call(new SettingsCall{});

interface IApiRequest<TRequest, TResponse> { } // Marker interface

class SettingsRequest : IApiRequest<SettingsRequest, SettingsRequest.Response>
{
    public class Response
    {
    }
}

static class X
{
    public static TResponse Call<TRequest, TResponse>(IApiRequest<TRequest, TResponse> req)
    {
        // TODO: ...
        return default;
    }

    public static void DoCall()
    {
        var response = Call(new SettingsRequest());
    }
}

RD>interface IApiRequest<TRequest, TResponse> { } // Marker interface

RD>class SettingsRequest : IApiRequest<SettingsRequest, SettingsRequest.Response>
RD>{
RD>    public class Response
RD>    {
RD>    }
RD>}

RD>static class X
RD>{
RD>    public static TResponse Call<TRequest, TResponse>(IApiRequest<TRequest, TResponse> req)
RD>    {
RD>        // TODO: ...
RD>        return default;
RD>    }

RD>    public static void DoCall()
RD>    {
RD>        var response = Call(new SettingsRequest());
RD>    }
RD>}
RD>

interface IApiRequest<TResponse> { } // Marker interface

class SettingsRequest : IApiRequest<SettingsRequest.Response>
{
    public class Response
    {
    }
}

static class X
{
    public static TResponse Call<TResponse>(IApiRequest<TResponse> req)
    {
        // TODO: ...
        return default;
    }

    public static void DoCall()
    {
        var response = Call(new SettingsRequest());
    }
}