Try select different color for drawing, not black оn white, and it will work.

enter image description here

This code works:

import SwiftUI
import PencilKit
import Vision

struct HandwritingRecognizerView: View {
    @State private var canvasView = PKCanvasView()
    @State private var toolPicker = PKToolPicker()
    
    @State private var recognizedText = ""
    @State private var isRecognizing = false
    
    var body: some View {
        VStack {
            HStack {
                Button("Recognize") {
                    recognizeHandwriting()
                }
                .padding()
                .background(Color.blue)
                .foregroundColor(.white)
                .cornerRadius(8)
                
                Button("Clear") {
                    canvasView.drawing = PKDrawing()
                    recognizedText = ""
                }
                .padding()
                .background(Color.red)
                .foregroundColor(.white)
                .cornerRadius(8)
            }
            .padding()
            
            Text(recognizedText)
                .font(.headline)
                .padding()
                .frame(maxWidth: .infinity, alignment: .leading)
                .background(Color.green.opacity(0.1))
                .cornerRadius(8)
                .padding(.horizontal)

            PencilKitCanvasRepresentable (canvasView: $canvasView, toolPicker: $toolPicker)
                .onAppear {
                    toolPicker.setVisible(true, forFirstResponder: canvasView)
                    toolPicker.addObserver(canvasView)
                    canvasView.becomeFirstResponder()
                }
                .frame(maxWidth: .infinity, maxHeight: .infinity)
            
           
        }
    }
    
    func recognizeHandwriting() {
        isRecognizing = true
        
        // Convert PKDrawing to UIImage
        let image = canvasView.drawing.image(from: canvasView.drawing.bounds, scale: 1.0)
      
         // Create a request handler
        guard let cgImage = image.cgImage else {
            print("Could not get CGImage from UIImage")
            isRecognizing = false
            return
        }
    
        // Important: Create the request with the recognition level set to accurate
        let request = VNRecognizeTextRequest { (request, error) in
            if let error = error {
                print("Error: \(error)")
                isRecognizing = false
                return
            }
            
            guard let observations = 
                         request.results as? [VNRecognizedTextObservation] else {
                print("No text observations")
                isRecognizing = false
                return
            }
            
            // Process the recognized text
            let recognizedStrings = observations.compactMap { observation in
                observation.topCandidates(1).first?.string
            }
            
            DispatchQueue.main.async {
                self.recognizedText = recognizedStrings.joined(separator: " ")
                self.isRecognizing = false
            }
        }
        
        // Configure for handwritten text
        request.recognitionLevel = .fast//.accurate
        request.recognitionLanguages = ["en-US"]
        request.usesLanguageCorrection = true
        
        // THIS IS THE KEY: Set recognition to handwriting mode
        request.recognitionLevel =  .accurate//.fast.
        request.recognitionLanguages = ["en-US"]
        request.customWords = ["o3Draw"] // Add custom words that might appear in your app
        
        // Very important - set this to true for handwriting
        if #available(iOS 16.0, *) {
            request.automaticallyDetectsLanguage = false
            request.revision = VNRecognizeTextRequestRevision3
        }
        
        DispatchQueue.global(qos: .userInitiated).async {
            do {
                let requestHandler = VNImageRequestHandler(cgImage: cgImage, options: [:])
                try requestHandler.perform([request])
            } catch {
                print("Failed to perform recognition: \(error.localizedDescription)")
                DispatchQueue.main.async {
                    self.recognizedText = "Recognition failed."
                }
            }
        }
        //---
    }
}

// PencilKit Canvas SwiftUI wrapper
struct PencilKitCanvasRepresentable: UIViewRepresentable {
    @Binding var canvasView: PKCanvasView
    @Binding var toolPicker: PKToolPicker
    
    func makeUIView(context: Context) -> PKCanvasView {
        canvasView.drawingPolicy = .anyInput
        canvasView.alwaysBounceVertical = false
        canvasView.backgroundColor = .clear
        canvasView.isOpaque = false
        return canvasView
    }
    
    func updateUIView(_ uiView: PKCanvasView, context: Context) {
        // Updates happen through the binding
    }
}
// For iOS 16+ specific optimizations for handwriting
extension VNRecognizeTextRequest {
    @available(iOS 16.0, *)
    var revision3: Int {
        return VNRecognizeTextRequestRevision3
    }
}

#Preview {
    HandwritingRecognizerView()
}