How to return either

Using generics and reflection to do a POST, then process the JSON, then return the correct type with its data.

Problem is that I won't know in advance if the type will be a single object or a list of objects. So my generic return type needs to be either a single thing, or a list of single things. (This is .NET Core 6, so what's why the ! in some places...)

How do I handle this conundrum?

    private static async Task<T> ProcessJsonResponse<TX>(HttpResponseMessage response, 
    string? returnModel = null)
    {
        var result = await response.Content.ReadAsStringAsync();

        if (returnModel != null)
        {
            var type = Type.GetType(returnModel);
            var obj = (T?)Activator.CreateInstance(type!);

            var test = type!.GetMethod("FromJson");
            object[] parametersArray = { result };
            var tim = test!.Invoke(obj, parametersArray);
            if (tim is List<T> nowwhat)
            {
               //can't return List<t> since the return type is T
            }
            return (T)tim!;
        }
        //<snip> other non-relevant code ...
    }