找出一个可能的答案，在Get请求的开始，我使用HttpContext特性中的DisableBuffering方法，现在返回的流是平滑的，没有延迟/缓冲。
不知道这是最好的方法还是正确的地方，但它已经解决了这个问题。

var features = HttpContext.Features.Get<IHttpResponseBodyFeature>();
    features?.DisableBuffering();

[HttpGet("{cameraId}")]
public async Task<ActionResult> StreamCamera(int cameraId)
{
    // Added this here
    var features = HttpContext.Features.Get<IHttpResponseBodyFeature>();
    features?.DisableBuffering();

    var camera = _context.Cameras.FirstOrDefault(item => item.Id == cameraId);

    if (camera == null)
    {
        return NotFound($"No camera found for id {cameraId}");
    }

    using var stream = await httpClient.GetStreamAsync(camera.cameraUrl);

    Response.ContentType = "multipart/x-mixed-replace; boundary=myboundary";

    await stream.CopyToAsync(Response.Body);

    return new HttpStatusCodeResult(200);
}