Question how to resolve problem in saving render texture to file as raw bytes?

I'm trying to save a render texture directly as raw bytes, instead of image, to discard image encoding and thus to speed up the process. However when I read the saved file and re-save it after encoding as PNG, to make sure I did the right thing, I see that PNG file is just blank.
What am I doing wrong?
probably irrelevant: project is on HDRP pipeline

This is the code I'm using to save render texture as raw bytes:

Code (CSharp):

1. IEnumerator StartCapture()
2.         {
3.             while (true)
4.             {
5.                 yield return new WaitForSeconds(0.2f);
6.                 ScreenCapture.CaptureScreenshotIntoRenderTexture(rt);
7.                 //compensating for image flip
8.                 Graphics.Blit(rt, renderTexture, new Vector2(1, -1), new Vector2(0, 1));
9.  
10.                if (prevFrame == null)
11.                 {
12.                     Setup(targetTextureWidth, targetTextureHeight);
13.                     Graphics.Blit(renderTexture, prevFrame);
14.                 }
15.  
16.                 flowMaterial.SetTexture("_PrevTex", prevFrame);
17.  
18.                 //calculating motion flow frame here
19.                 Graphics.Blit(renderTexture, flowBuffer, flowMaterial, (int)Pass.Flow);
20.                 Graphics.Blit(renderTexture, prevFrame);
21.        
22.                 AsyncGPUReadback.Request(flowBuffer, 0, TextureFormat.ARGB32, OnCompleteReadbackNew);
23.             }
24.  
25.         }
26.  
27.  void OnCompleteReadbackNew(AsyncGPUReadbackRequest request)
28.         {
29.             if (request.hasError)
30.                 return;
31.  
32.             var bytes = request.GetData<byte>();
33.  
34.             WriteTextureAsyncNew(bytes);
35.         }
36.  
37. async void WriteTextureAsyncNew(NativeArray<byte> bytes)
38.         {
39.             imageCount++;
40.    
41.             filepathforflow = customOutputFolderPath + imageCount + ".txt";
42.             await File.WriteAllBytesAsync(filepathforflow, bytes.ToArray());
43.         }

This is the code I'm using to read the saved file and re-save it as PNG:

Code (CSharp):

1. var newBytes = File.ReadAllBytes(customOutputFolderPath + "5.txt");
2. var target = new Texture2D(targetTextureWidth, targetTextureHeight, TextureFormat.ARGB32, false);
3. target.LoadRawTextureData(newBytes);
4. target.Apply();
5. var lastBytes = target.EncodeToJPG();
6. File.WriteAllBytes(customOutputFolderPath + readCount + ".png", lastBytes